I had problems with milk supply with my first baby and want to do everything possible to ensure I have a good milk supply this time around.
Unfortunately, I don't know of anything you can do during your pregnancy to increase your milk production for when the baby is born (besides eating healthy foods!) I can assure you that many mums who had problems nursing their first baby have a much easier time with the second. The best way to prevent problems is to educate yourself beforehand about the basics of latch on and positioning and what to expect when the baby is born. Also have a good support system in place in the event that problems do develop.
I don't know what kind of support/advice you had before, but if you gave up on nursing because of low milk supply, then something was wrong. There are only a small percentage of mothers who can't breastfeed, and most of the time this is due to medical problems that can be corrected. A good lactation professional will be able to work with you to discover the cause of the problem and make recommendations to fix it early on, whether the problem is soreness or low supply or whatever.
It is very important to have a good support system in place so that you will have someone to call for advice at the first sign of problems. Find out if there are any lactation consultants (IBCLCs - International Board Certified Lactation Consultants) in your area. These are healthcare professionals who have received extensive training in lactation, above and beyond the training that doctors or nurses receive. They are the only members of your baby care team whose focus is primarily breastfeeding. Most major hospitals have IBCLCs on staff, and some IBCLCs are in private practice.
What is relatively new to the market is a wonderful product called Qiara Pregnancy & Breastfeeding Probiotic. Unlike many vitamins and supplements Qiara is backed by medical evidence. It is a probiotic that is originally found in breast milk and it has proven extremely effective in many women assisting in breast feeding and assisting in the prevention of issues such as mastitis. It also has many benefits for baby too. Popular press has highlighted the product in recent months and is now becoming popular with those who export such products which are popular with Asia parents, so its not always easy to get any more. If you get your hands on some then it is well worth giving it a go.