When I started riding fixed I was already very comfortable with the bike.. It was a SS and I rode it for a good month before I rode it fixed. That definitely helped. I've thought about this some and here is my basic advice to a new fixed rider:

1) ride the bike SS for a few days first if possible; get used to the handling of the bike
2) Make sure you can already use the clips or clipless pedals, and you MUST have these when you start riding fixed. It isn't just for skidding or stopping; your are very likely to "forget to pedal" at a high speed and this will help keep your feet on the pedals and keep the pedals out of your shin/leg. If you can't use your foot fastener SS don't ride fixed until you can.,
3) don't remove the rear brake just because the bike is fixed. a new fixed rider must demonstrate the ability to stop the bike with pedals before taking the rear brake off; IMHO (flame on)
4) under no circumstance remove the front brake unless you have ridden fixed for a significant time.

From then, I don't know. The hardest part for me was learning to start from a stop. Perhaps you want the seat a little lower to start so you can put your foot down on both sides while on the saddle. Do this just long enough until you can start and stop. Of course, as you are riding don't stop pedaling. This will haunt you when you switch from freewheel/fixed but over time your legs become supple when you forget to pedal, at least mine did.. I ride every day for transport, and it took me about 2-3 hours of riding fixed to feel very comfortable on the bike(with front/rear brakes). It took me another week to develop the natural feeling of always pedaling, but at that point if I got up to speed and started to coast my legs would be supple and ready to spin and it wasn't a problem.

Just keep at it, you'll get it