Some women who start out breastfeeding but within a few months or sometimes weeks get discouraged, ween their baby, and switch to formula. The list of reasons ranges from insufficient milk supply, infections, or sore nipples to criticism, or confusion about what they should be doing. Most of these problems can be avoided or at least minimized by having a good support network.
First be sure to include your partner and your family in the decision to breastfeed. As they are the ones (aside from your new baby) with whom you will be spending your time its a good that you are all working together.
Next on your side should be your pediatrician and lactation consultant. Having your doctor be supportive of your breastfeeding choice will make many of the physical aspects easier as they will encourage you to continue and not simply point you and your baby to the bottle.
Friends and presently nursing mothers also offer much encouragement. It is hard to day anything on your own, so having others whose advice you trust will make it much easier. Yo may find meeting up at regular times for social interaction while you breastfeed will do wonders for your morale (especially when you may be experiencing conflict in other areas of your support network) Having and making friends of other breastfeeding mothers will also help introduce your child to other playmates as they grow.
Lastly groups like La Leche League or local pro-breastfeeding groups can be a great way to meet new people and get additional ideas for some of the less common things you may experience.
However you build your support network is up to you, it is only important that you do so before problems and questions arise. Nothing can be more discouraging than feeling alone in any adventure.