Beginners often have a hard time knowing what to work on first. The short answer is, keep it simple. However, knowing what to practice is really only half the battle. The other major component is finding the time to practice.
If you’re only practicing during class twice a week, perhaps you should consider practicing more often. Practice should be on a regular and consistent basis. As we all know, you can’t wait for free time. It just doesn’t happen. You have to schedule it in if it’s important to you. I recommend practicing at least two additional times during the week for at least 15 minutes each time. If you can do twice a week for 30 minutes, even better.
As for what to practice, there are a lot of trains of thought. To keep it simple, pick one thing and work on it over and over until you can move with confidence with it. This could be a form, set, technique or what have you. Don’t get too crazy with too many things as you won’t be focusing your time (rifle vs. shotgun approaches). You can work on techniques from one belt level, going down the list and performing them in the air. Have a bag or a “Bob?” Work your techniques with full speed and power 10-15 time each within one belt level. You can also practice a form and do it as many times in a row (with or without stopping) in the time frame you’ve elected to practice. Practice it once slow, once for show, and once for the street.
Remember, you don’t need to practice with your gi on to practice the martial arts. All you have to do is make the time on a regular and consistent basis, focus your efforts, and stick to it.