The more practise you do the better you will get. Just think about all the time you spend watching rubbish on TV; this is perfect drum practise time. In truth, if you put in 15 minutes a day you will improve. If you put in 30 minutes a day, you will improve more and so on. The most important thing is to keep focused and work on the things you can't do as well as those you can do. It's common for younger students to require a little parental coercion to get them practising. Those aiming to progress rapidly should put in about 1 hour (or two 30 minute sessions) a day.
Playing to a song you like or to a metronome can be very beneficial as this will help improve your timekeeping skills. Just make sure the tempo isn't 'blisteringly fast' or it won't help at all. Counting aloud is also something worth practising to keep your playing even.
It's always a good idea to warm up at the start of your practise session; first try the single stroke roll (RLRL) remembering to hold your sticks the correct way and to keep your wrists loose. Count as you go.
This useful guide on practising from musicteachers.co.uk might be helpful.