It's a huge amount of info to take in in a short amount of time. The time in the sim goes very quickly, you are continually learning new things. Just a matter of keeping up with what you are learning. ATC is very fluid, no two conflicts are the same. I think people that 'learn' conflicts in the sims, as opposed to understanding the rules and applying them to solve the conflicts end up falling over. Being confident in each transmission is also a must.
As your driving home, watching tv, in the shower, think up conflicts and as many ways as you can to solve them. If you can look at a conflict and think of 3 ways to solve it, you won't have any problems.
On top of that, sim exams can be quite stressful. If you make a mistake, don't let it get on top of you, keep clawing away and hold onto at least one form of separation. Furthermore, each exam is designed to cripple you with conflicts and problems.
No greater feeling than finishing up a sim exam, getting called into the room and told you passed.