M.
Here's a great resource on all of the different weaning options:
http://www.kellymom.com/bf/weaning/how_weaning_happens.html
And as far as planning on having him off breastmilk by 12 months, is there any reason you want to do this? In case you've never been encouraged to keep going, did you know that YOUR milk (human milk for human baby) is far more appropriate, healthy, and good for him, even at 12 months or 18 months or whenever you both are ready to wean, than any milk you might wean him to right now at 12 months (say, cow's milk for example, which is cow breastmilk intended for baby cows - the makeup is appropriate for baby cows, much less so for baby humans). Despite what any doctor or well-meaning relative might try to convince you, there is NO reason to wean your baby by 12 months - the health benefits for you (reduction in cancer risk and diabetes risk) as well as for your baby (too numerous to list here) last for as long as you continue to nurse. It is entirely normal, and biologically VERY expected (normal for our species), to nurse well beyond 12 months old if you and your son are enjoying the nursing relationship.
If you are ready to wean him, and you are sure that cutting down on nursing would not be an option you're interested in, you can certainly gradually wean him, though I truly wouldn't start that process until he reaches his 1 yr birthday - the American Academy of Pediatrics even states the breastmilk should be the *majority* of your baby's diet for at least the 1st *year* and even beyond if you and your baby are able and willing. At 12 months, if you want to wean, you can just gradually decrease the length of one nursing session by a few minutes each day until you've eliminated that feeding entirely, and continue to do this until there are no nursing sessions left. That will typically be most comfortable for mom's body (no hugely engorged breasts) and gradual/less abrupt/shocking to baby. However, you know yourself and your baby best - you will find the best way that works for the both of you, I am sure!
And a huge, huge congratulations for breastfeeding for 8+ months - our entire population would be more healthy if all moms committed to doing what you have done for yourself and your baby (and our environment) by breastfeeding! Yay, you!