If you can, buy or borrow the book Healthy Sleep Habits, Healthy Child by Dr Weissbluth. If you have time, read the whole thing, if not, at least read the section for you son's age range. It has lots of great information, but be warned, he knows alot about sleep issues, but he isn't the greatest writer. Also, take the testimonials with a grain of salt. Every kid is different and most kids don't sleep through the night after one or two days. :)
We used modified versions of his methods with our daughter, 3 years old, and our son, 5 months old. I say modified because every child is a little different and develops at different rates. We started "sleep training" with bedtime only. We would have our bedtime routine (bath, massage, book, prayers, snuggle) and then put our child in the crib to fall asleep. There was alot of crying/fussing in the beginning, but after a few weeks there was hardly any fussing before they'd go to sleep. I then followed the rule that I would go to them at night, but I wouldn't rush right in when they fussed. I found that often, they'd wake up and fuss for 10 or 15 minutes and go back to sleep. If they were really crying, I went right in to them and helped them back to sleep if needed. If they seemed hungry, I nursed them. Weissbluth even says in his book that some children may need night feedings up to 9 months old. My daughter still had one feeding a night until she was 9.5 months old and my son still wakes for one feeding.
If your son is waking often at night, he might be waking when he enters the light sleep phase (every 45 min to an hour), or he could easily be hungry. At his age he could easily need to eat once, and if you are nursing, he could need to eat twice. Don't be afraid of responding to him at night for now. Work on one thing at a time. Get him used to going to sleep on his own at bedtime. Once he has that figured out, you can work on the middle of the night.
Another area to focus on, if you aren't already, is daytime sleep. If babies don't get enough daytime sleep, they become overtired and that affects night sleep. You should also have an early bedtime, no later than 7 pm and often earlier for a child his age.
When you are ready, work on the middle of the night wake ups. I was never comfortable with not checking on them. As I said, with light crying/fussing, I would wait at least 10 minutes to see if they'd go back to sleep. If they were crying, I would always go check on them. If they needed to eat, a diaper change, a snuggle, whatever, they got it. When my daughter was about 7 months old, I would go to her, but after a little bit, I would put her back into her crib to go back to sleep. I wanted her to know that I would go to her if she needed me, but it was nighttime and time to go to sleep. She wasn't too thrilled, but soon she was going right back to sleep.
Good luck! Hope this helped a bit.