Get the basics down before you start playing with combos and different technique. Listen to your coaches. Coaches are always busy in a good gym walking around helping people. Fighters getting ready to compete get A LOT of attention from trainers/coaches, and that takes some away from you.
The best thing you can do is ASK. You need to be able to ask someone (a coach OR an experienced person, whoever is available at that second) if you are doing something wrong OR right. When your coach gives you something to work on (like certain strikes, footwork drills, whatever) than you just work on that until he/she gives you something new to do. It's that easy. You don't want to get bored either, so in between practicing whatever they are having you work on, you can skip rope (takes a while to get good at, so use it to fill time and warm up), practice the speed bag (like skipping rope, it's not something someone can really teach you, you have to just get used to it), or whatever.
The bottom line is that a coach/trainer/partner/whatever can show you what to do, but you have to just get in and practice it. IT TAKES TIME. You will NOT have someone there standing over your shoulder the whole time. You need to know what it is you are working on, ask questions in between, and keep at it. I always have a list in my head of what I need to work on and those are the things I practice in the gym. If people are available I get them to hold mitts, pads, spar, or whatever. There are classes, but training in fighting is a very self-motivated self-driven thing.
But get your "base" down first. The worst thing is learning something wrong and having to re learn it. If you jump too far ahead you will be making a lot of mistakes. Good luck and enjoy!!!