I will describe what I have found to be important in regards to hip hop dancing from my experiences as a beginning student. I will hopefully encourage you to take up hip hop, because if at the age of 29 I was able to begin lessons and get a few moves together, then absolutely anyone can do it! I have never danced before and have absolutely no skills at all.
So what is important?
1. Feeling the beat of the music.
When you are beginning, it is easy to get lost in trying to get the moves correct, and forget that you are actually dancing to music. I was like that at the start, and it makes it less enjoyable and actually more difficult to get the moves happening. You will find that as you progress even just a little bit, that you make the best progress in learning moves when you are feeling the beat and moving to it.
2. Remember to bounce.
Most moves are done to the beat of the music, as described above. Almost always, the timing of the moves involves bobbing your head, and bouncing your body "up, down, up, down, up, down" to the beat of the music. All of the moves beginners will try to master early, everything from the two step, to the running man, all need to have the concept of "the bounce". If you don't have the bounce in your moves, you'll be dancing stiff and upright and will look strange. It is also a bad habit to get into, and if you are not bouncing, the moves are not timed well and it will be almost impossible to the music in any way that looks good.
3. Warm up and Stretch
Warming up and stretching should be a part of every session. As you learn, take note of the stretches and isolation exercises your teacher takes you through so you might use them when you practice or elsewhere. Without a proper stretch you can injure yourself, or not be loose and ready well.
4. Put a routine together
Moves should come together in a sequence, otherwise you will be doing the one thing repeatedly, or just randomly starting the next type of move as you go. If you practice your moves in a routine with steps that lead in to the next move, you can then store these transitions through practice and can use them in the future when you are dancing. With a few different transitions, you'll be able to dance smoothly for short periods of time quite easily.