Set a good example
In my experience, this is the baseline for almost any personal cycling advocacy.
Be available to help
Make it clear that you're available (but not pushy) to help any friends/family with cycling.
A challenge to get them in the habit
My regional bicycle coalition does a Team Bike Challenge as part of Bike to Work Day/Month. They change the rules each year, but basically your team earns points the more you use a bicycle for transportation.
A couple years ago, I "captained" a bike to work month team and got a few of my co-workers onto the team. This requires identifying people who are likely cyclists who could possibly be convinced to bike commute regularly. My team also had another person who already biked to work regularly during good weather. A couple of those team members are now regularly commuting to work on their bicycles, and one of them helps out at the local bike co-op type place now, too.
I think the two key aspects of this are:
- Making it competitive provides motivation to do it day after day
- Doing it day after day makes it a habit. Once you're in the habit, it's really no harder than riding to work.
A very close personal relationship
(borrowing a bit from moz's sexier answer on the original version of this question)
It can take several years. It's a very slow conversion process. Seems to have worked with freiheit♦'s current girlfriend, and with 2 of moz's girlfriends.
I think the fact that it's an activity you can do on your own, with your life partner, or with random acquaintances helps a lot.
- Find a potential mate/girlfriend/boyfriend/spouse who is a potential cyclist
- Through years of relationship, set a good cycling example
- Help them get a bicycle (buy for them, help them shop, whatever) when they indicate interest (don't push)
- Help them with any issues that come up. Fix a flat now and then, work on the bike (or get it to a shop) when maintenance is needed. Help them get the right accessories, etc.
- Help them get that second bicycle when they figure out that the first one wasn't quite right
- Help them get that third bicycle when they think they've finally got everything figured out just right.
Put your children on a bike as early as possible, first on a child seat on your bike (as soon as their head stands, 8/9 months) then on their own bike (3/4 years). Go to school by bike with them. Sooner or later, their mother will be converted as well.