Any mothers out there with potty training tips?

My son will be 3 in June and we're half way there with potty training. He'll tell me if he has to poop but he'll keep peeing in his pull ups or underwear. I put him on the potty every half hour and he goes almost every time but he still has accidents through out the day which I know will happen with toddlers. He was 6 weeks premature so I'm not sure if that has anything to do with it but I'd like to have him fully trained by the time he's 3 and I feel like there's something I'm not doing. Please help!