tips/tricks, it doesn't matter. you need idea, how your tactic should work.
how you create a ball transition, how your team should be possessed on the opponent area of the pitch, etc.
why you wanna play 3 at the back? if it based on your teamsquad, mb better to buy fullbacks. 4 at the back more easier to setup.
the biggest problems with 3 defenders formation lies in match engine.
DCL and DCR in possession always stays in centre. give them "free role", loads of creative freedom, "move into channels".. nothing changes. how defensive line look in 3-5-2 in possession fm10 match engine:
it's terrible ,because when your DCR/L get the ball, he are limited in the options:
a) your MR and ML always be marked by opponent winger.
b) you can try to pass to the one of MC, but he constantly be on closing down, and he have a little time to make desision.
MR/L also plays more like defenders, than like wingers.
counterattacking 3-4-3 should work.
try something like this:
passing: default or direct.
push your defence line a little bit up.
vital here: 1 of your strikers(most creative) shoul be in support role.
3 at the back its painfull path. you will see things like this
very often, before your defence learn how they should play.
but, excluding all this cons, this formation in right hands -solid in defence.
this is my team, 3-5-2, one of my players is sent off, and we play 10 vs 11.