Well I wanted to help the guys out who are interested in this stuff. I'm going to share my knowledge and help you guys to start with this hobby.
Metal detecting is illegal in loads of places and some countries so if you head out to an area where it's illegal to dig prepare yourself!! Always strive to ask for permission from the land owner, don't be a jackass!
For example in Germany it's always illegal to dig unless you have a permit, the fines are really high you can even end up in jail...
First of all you need a metal detector (DUH)
For beginners, it is recommended to use something like a Garrett ACE 250 or a Garrett Euro Ace, those two metal detectors are rather cheap (250-300$) and easy to use but most of all they work! You could also invest in the Garrett AT Pro (or AT Gold which is basically Pro+) which is twice the price but is a lot more powerful and versatile, this is the case especially if you know you're gonna be sticking with this hobby for a long time, might as well invest from the start.
Another very popular and absolutely excellent detector is the XP Deus, which many say is the best detector on the market as of now, beating the AT Pro for example in target separation. It's slightly more expensive though.
There are many other brands, including Minelab, Golden Mask, White, Fisher, Makro, etc.
All the above detectors are VLF (very low frequency) detectors. There is a second type called Pulse Induction (PI) detectors:
For something like prospecting gold nuggets in the Australian desert, and gold prospecting in general a PI detector is pretty much mandatory and is what they are used the most. For finding coins/relics/artifacts in parks/fields/forests etc, aka what 95% of us do, VLF is king.
Here are animations for how VLF and PI work:
How VLF detectors work
How PI detectors work
The coil in your detector matters! There are several different types to choose from, and install/switch on your detector.
DD coils have a narrow but wide detection field that make target separation easy. Wider field compared to concentric coils, allows for larger area to be scanned per sweep. Generally regarded as the jack of all trades, best choice for most areas.
Concentric coils are the classic large circular coils that punch into the ground with a cone-shaped field. Bad in trashy areas because of the cone-shaped field, but work well in open, rural areas.
Sniper coils are very small circular coils that are great in trashy areas like heavily used parks. They allow you to "snipe" targets from the middle of trash, with a thin and sharp detection field. Think of it like stabbing a sword into the ground to hit a coin, compared to a wooden log that will hit the coin and 5 bottlecaps around it. Downside of sniper coils are the bad search depth and small scan area per sweep.
All of these coils come in various sizes that affect their search depth, weight, and target separation abilities.
I mostly use a hand shovel, a hand saw can come in very handy to cut through tree roots in your digging area. In addition to the main shovel, you might want to keep a small gardening trowel for precision digging, since it's annoying to handle a large shovel when checking the hole for your target.
Pinpointers are EXTREMELY USEFUL. Essentially mini metal detectors, they will show precisely where in the hole your target is at, saving a lot of time and pain. No more shifting through a bucketful of dirt to find that 1 penny, a pinpointer will point you right at it. The best on the market hands down is currently the Garrett Pro-Pointer AT. Currently $127 on Amazon, it's an absolute necessity for any metal detectorist and an investment you won't regret.
Whatever you want, gloves are a must though unless you like blisters on ye fingers.
A small bag on your waist for holding artifacts/relics/coins/whatever you dig up is recommended.
UXO's ( Un-exploded ordinance)
Don't be careless guys, always do research on places before you go metal detecting. 70 year old mines can, and in most cases, are, still functioning. They're soldiers that never realized the war was over. They're not like the movies either, 95% of landmines you will never see until you step on them, the other 5% have been revealed by erosion or rain washing them away, which means even areas that aren't minefields, but downhill from them, can have mines that were washed away, which will still be active most of the time.
I guess the best way to show what I mean is this picture. A burnt-off, mostly barren area would easily be the best place to see a mine, but you still can't see shit in this image. It's somewhat low quality, but that's pretty much how your vision will be if you're only paying attention to your metal detector.
There weren't many made in WW2, but there are low-metal mines too, which means your detector wouldn't even detect it. So the only real advice I can give is to do your research, and leave the area, on the exact same path you came, as soon as you see any kind of mine indicators. The most obvious ones are keychain looking objects with 30+ arming pins on them, and metal tubes, sort of looking like a disposable launcher, like a panzerfaust, but wider. They were used to contain mines. Less obvious things include metal or wooden spools, used for tripwires, or individual arming pins. Everything else will just look like normal wartime junk, especially after rust and such takes their toll on them, so there's no real point in describing them. Just be safe guys!
The most important step of all is research, its not likely that you are going to find interesting items without researching first.
You can use all kind of media for this, books, the internet and old people who might know something. For my trip to Schönberg (http://www.facepunch.com/threads/1123012) I mostly used the internet, google maps is also a good idea.
For finding coins and jewelry, hit your nearest park and/or beach. Note that most low-end metal detectors are not waterproof, so be careful on the beach.
Research nearby abandoned house sites and old farming fields, since you can find some great stuff in there including both coins and relics.
If you are looking for military relics you best search for battle maps of some kind. They hold loads of information and can really help you out. On-site, look for strange pits or dug outs in the landscape, as even after 70 years you can still see the foxholes and the trenches. Those are a good place to start.
One of the maps I found for my Schönberg trip, and a picture of old foxholes as an example:
Also urundeadmom wanted to add this:
Its also important to look for trees, like for example if you have a hill that has only 1/2 meeter high grass, and you find a large group of young trees growing somewhere, that means that the soil has been moved around for a trench or bunker, its most likely a trench, several times i have seen areas that have a about 20 m long line of young maybe 3-4 m high trees that was once a trench.
The best places to look are wet marsh like areas with A LOT of mud, the mud creates a almost oxygen proof seal that preserves items incredibly well. Regular dirt will hold items considerably worse with a lot of oxidization and rust occurring. Sand and dirt-sand mixes are the worst with items quickly deteriorating and no noticeable markings left on them.
Old house sites are treasure troves for coins and relics, along with farming fields (always ask for the owner's permission).
Cleaning your items:
Most of the time it's enough to gently brush the rust off, you can treat your finds to prevent more rust forming.
If you have a really rusty item that is still hard and not rotten you can use a solution of oxalic acid to remove the rust, this again is at your own risk, as you can destroy your item.
If you find an old coin, be extremely careful with cleaning! Do not remove any beautiful patina, as that will degrade its value! Method 1 is to use a toothpick to gently rub most of the dirt off, but leave some dirt at strategic spots to highlight the details, that's usually all you need to do. Another popular method is the soft toothbrush+soapwater treatment, but it's not always the best option since it can remove details and patina from older coins, and can get rid of highlights. On some coins it is enough to simply rinse them with water. Leave the rest to a professional if you even need to! Very old finds like viking age silver hammered coins can be fragile as fuck, even rubbing them between your fingers can cause them to snap in two so again, be careful!
AWESOME FINDS: (These are finds of many different people.)
-Always dig around the signal! You don't want to stick your shovel into a grenade or bomb and you don't want to damage the items you dig up. EXAMPLE by Orkel's hasty friend: 1890's silver pocket watch ruined by digging too close
-Please fill up your holes after you dig and also don't leave any garbage behind.
-If you find an explosive don't move it, leave it be and call the bomb squad/police. Some WW2 explosives, due to the time they've degraded in the ground, can blow up just from being exposed to air after digging it up, or vibrations from your shovel.
-If you don't find anything, don't worry, keep on searching you'll find stuff eventually. Note that equipment matters, cheap detectors generally have bad search depths and can be unreliable at separating good targets from rusty nails.
-Digging is really exhausting, always bring enough food and water.
In this thread you can post your finds, ask questions etc...
You can ask me anything you want!
If anyone wants to add something to the op just pm me.