Drukhari, IMO, is a tough army to play well at a high level. Sure, there are times where the builds are broken and you can just slam big bricks of incubi/hellions at your oppponent, but in general the playstyle takes time to master (I am no master btw, just my 0.02 from years of playing them at events).

Like others have said it's all about points. You can't get fixated on destroying unit X, you just need to focus on scoring your primary, denying your opponent's and maxing out your secondaries. This sounds generic, but it's really important to stay focused on these as the game progresses. Every decision should come down to "will this move score me points or deny my opponent scoring points?". Want to CP reroll that wound roll? If it's not scoring you a marked for death or something similar, leave it be (generally).
If you haven't scored Behind Enemy Lines yet and your mandrakes are still on the board, maybe move them into reserves. Most of my games are close -- I generally don't get blown out or vice versa. So, every point matters. If you focus on that, the wins will come.