Tackling.......sorry, couldn't resist.
Press helps but can leave you vulnerable for certain pass routes, especially deep.
Manually moving a safety up then switch to whatever player you normally user works for me as safeties don't automatically return to original position like LB's do.
I use 3-4 D, crashing line left or right [only if your sure of up the middle run] confuses blocking momenterily. User an LB opposite the crash to contain potential cutback.
I prefer to user the weak side inside LB in 34, depending on down and distance and play called. If offense is in two back set the WILL LBs assignment is usually the HB for man plays. In this case, back off a little and use strafe or defensive assist if your not yet a stick jockey.
For single back sets your assignment varies, check it with play art then be prepared to cover a TE or back coming out of the backfield if thats your assignment, once the ball is snapped if its a handoff go to the ballcarrier. Again, strafe helps, resist the temptation to mash the right stick/sprint as this usually leads to instant engagement with blockers.
For zone plays of course cover your zone assignment but be ready to react to the run/ballcarrier as play develops. An option on zone plays is to spy the usered LB which gives you a little edge on run reaction, if you see pass move to your original zone assignment.
On MLB zone blitz combo's I prefer to user an outside LB and go with whatever assignment the play has designed. If I choose to user an inside LB I either back off and spy/react to pass or run or stay in blitz but back off and follow the other LB or Dlineman through the gap effectively running around or between other defensive players engagements with blockers. This often leads to big plays if used sparingly.
Have also had success moving up and taking on the blocker allowing the cpu controlled LB to hopefully get through.
Don't count on proper LB gap assignment as it is poorly programmed to say the least!!!!!!
If you have a fair understanding of LB gap assignments you can use it somewhat effectively with practice but only with the player/LB you are controlling.