I prefer to make notes and learn them... There is not shortcut to study--rember that.
Copy notes you made in class/lectures, so they are readible (copying will aid you in memorization).
Then set an alarm clock for half an hour, and memorize your work with any method you like (it is just like memorizing the Koran/Bible). After half and hour, you have to do a progress check--did you learn any thing... or didn't it go to well... IF it didn't go well, then you take a differnet piece you have to learn and come back to the other piece later.
Now you are entitled to a 5-10 minute break--set a timer for this, too so you DO NOT go over your limit.
If you aren't good at mindmaps, then I don't recommend you try them--I have tried them and they are frustrating--just my opinion. Mindmaps make your page beautiful, but don't help you learn... Like I said--> there is NO short-cut to study.
If you have to give up time with friends to study, then don't feel sad--it is one of those sacrifices that turn out to be the best option for you.
The best study technique I have ever used, is to visualise what you are studying. Paint pictures of the facts in your head--even if they are silly--and you will be amazed at your abillities.
Another trick is read the Bible/Quran. God will unlock your mind!

I am not joking.
I pray God will help you with all your studies. I am on holiday now, but I will also be studying soon, so pray for me, too.
Matthew 7:7 "ask [God] and you shall receive; knock and the door will be opened to you".
Matthew 6:33 "Seek the Kingdom of God above all else, and live righteously, and he will give you everything you need."