Dont put C4 on your own team mates because when you detonate the bome you are bacicaly giveing away there location (not good for SBHs)

Also the AGT/Ob does not need 30 mines placed all over it, just 3:

AGT
1) in door way
2) a little closer to the MCT (NOT on it)
3) in the corner by the door (enemy seems to go to the left corner more than right, and they get time to detonate there C4 and change weapon too

Ob
1) In door way
2) left of the door way (where they allways hide to detonate there C4)
3) By MCT (NOT on it)

There is no need to put mines on top of each other in one big pile:

Apc rush with 5 Techs come in and get in your PP and all your mines are in one big pile (about 6-7 mines) Tech 1 gets in first and runs in and is blown up THEN Tech 2, 3, 4 and 5 have a clear path and blow up your PP (that happens to me all the time with n00b mine layers)

You need 3 mines per door per building (i.e PP needs 6 mines and the AGT need 3) that should be perfect and in building like the PP dont put 3 right on the door step... put a few closer to the MCT to.

Also (mainly flying maps) It is a good idea to put a mine or two on the building ramp because it takes quite a while to get to the top of the Weapons factory to disarm a beacon.