There's lots of great tips on here. I would suggest jumping into the group classes. Most often BJJ students are ultra nice and very helpful in making you feel comfortable. Here's a couple of things that may help you improve quicker
1) During sparring, if your sitting out for some rounds, be sure to watch the students roll, even better watch the Instructor and higher belts roll. You won't pick up alot of the techniques that way right now because you are now but you'll start to create a mental picture of what good BJJ technique looks like.
2) After class, take the time to write the techniques you learned that day using a lot of detail. The process of writing and thinking through each motion will help you retain the info better. You can also then spend some time, at home, during free time at work or any other time, reviewing those techniques in your mind while reading your notes.
3) Outside of class, try to explain and breakdown the movements you learn to a family member or close friend while at home. This again will help you retain the info. The next time you learn that specific technique you may realize that in your notes or breakdowns you were missing a detail or two. Adding them in at that point will be very easy.
Good luck man!