In my two years of being a parent, most of the people I learn are pregnant are on subsequent pregnancies... and most of the time people just do whatever worked the first time around (formula or breastfeeding). I have yet to have the opportunity to get someone on the first time around... but I'd like to think I'd be a lot of help to that new mom.
Generally Facebook is the place where I learn that distant acquaintances have just had a baby. They'll toss up birth announcement and newborn photos that get my attention. I usually drop a "congratulations, let me know if you/she needs any help with breastfeeding. I have lots of resources and experience" on their wall. I have yet to have any takers, and I don't know how many of these people have chosen to feed their baby. I'd like to get some confirmed success stories under my belt... so let's start getting proactive.
Perhaps a generic email is a good place to start. Having an already written up email would make it easy to give a "heads up" for support and tips to even the most random parent you know. For people closer to you, it would be easy to edit in some personal information. Having an email ready to go would be helpful in our busy lives, because as soon as you get wind that anyone is expecting - you can copy, paste, send and move on with your day.
Baby Showers is another place to take a step towards supporting this new mother-to-be. Giving a nice basket with nursing pads, LLL information, books etc.