I believe the most efficient way to keep on your top of your Chinese is to practice, practice, practice! This is definitely easier said than done, but it really comes down to self will and motivation. The more you practice, the easier it will become to learn new characters. You need to practice every aspect of Chinese - reading, writing, speaking - in order to see progress.
2. Every day, not every week
Organise your week so that you allocate time to practice Chinese. It's easy to put it off and tell yourself to do double the amount of study to make up for today, but when tomorrow comes around you will probably postpone it again. It's much more effective to do a little everyday than one big weekly session. Start with 15 minutes a day (while you're waiting for the pasta to cook!) and slowly work yourself up to longer study sessions. You'll retain more of what you have learnt by doing a little every day.
3. Cultural immersion
Enjoy learning Chinese! There are some fantastic Chinese dramas and movies. Chinese reality TV shows are also extremely entertaining! Chinese TV shows and movies generally always have subtitles on them so it is a great way to test your character knowledge too! It's a good idea to learn a few Chinese songs too so you can go to a karaoke bar when you visit China!
4. Pen Pal/Study Buddy
Having a pen pal will drastically improve your Chinese. You will constantly be thinking about sentence structure and how to phrase things. Your pen pal will be able to teach you common phrases that may not necessarily be in the textbook. It's great to practice with a friend too to practice your speaking. When you start feeling stressed out by speaking only in Chinese, you can use English words here and there, just as long as you're constantly using some Chinese!
5. Let it all out
A fantastic way to improve your Chinese is to keep a Chinese journal and write about anything in there in Chinese. Even if you can't remember the characters, you can write out the pinyin. The most important thing to gain from this exercise is to think in Chinese. Sometimes when I'm at home alone I will say what I'm doing out loud in a language I'm trying to learn. For example when I'm cooking I'll say what ingredients I need and how I'm going to cook my meal!