I'm by no means an expert but here's some pointers:

1.The closer to the enemy base the better. I'm not saying try to get them into the spawn. Seems a tad unsporting to me. But somewhere between their spawn and the closest flag to their spawn is ideal. Most people have their guard down or are over confident straight out of their base. They are eager to get to the action and are less observant.

2.If you're getting stomped and the other team has aggressive tankers, sometimes it pays to do the opposite of the first point. Put them near your nearest flag or on the way to it. Like any weapon, being aware of the flow of battle is key. See armour coming from A? Place mines on the approach to B. Or why not lure them in to a mined position with a rocket or two?

3.Don't just leave them on flags unless you've got a good reason. Flags get bombed to shit and grenades get tossed around like they're going out of fashion. Your mines won't survive. Place them just outside of flags. Particularly at points where YOU would drive up to the flag if you were in a tank. Tanks need cover too. Put them behind likely cover near main roads.

1. Concealment. Puddles and water crossings are great. Craters are better because craters can be created. Always put them on the lip facing away from where you think enemy armour will come from. Harder to detect and harder to destroy.

5.Someone else mentioned that two mines together is an instakill on all regular tanks. This is good advice. I always put two mines closest to enemy approach and my third mine further down the road. The reason being that if I disable a tank with one, I don't want them being alerted to the possibility of other mines in the area. I want that tank dead. The third mine is a bonus disable or destroyed light vehicle.

1. Mines are versatile. Arty truck camping on a hillside that isn't aware of your presence? Two mines close to it, detonated with a pistol or smg and bye bye arty truck or tank or whatever. Trapped in a building with enemy infantry running up the stairs? If you place a mine on the stairwell and camp (pre-sight) the mine you can bring the stairs down. Snipers holding a roof on Sinai or Suez? Bring the building down with AT mines. It's a poor man's dynamite is what I'm saying

2. Mines also resupply VERY fast. Almost as fast as primary ammo. So don't be stingy with them. (just hope your support isn't being stingy with ammo)