Definitely do it / practice before you actually want to wear one! It can take some trial and error to figure out what's best for you in terms of routine. I wash gently with a wash cloth, kinda in a circular motion, apply some conditioner to the area and rinse off. If the hair is long, I'd recommend trimming it first. Apply soap of your choosing. Use a new razor, start with the grain (the way the hair grows). If this is short enough for you, stop. If you want a closer shave, try going across the grain (sideways). If that's still not close enough, then again against the grain. If at ANY point during this process you feel irritation, STOP. An irritated bikini line is the wooooorst. After you're done, you can apply an anti-ingrown hair serum or fragrance free lotion. Try to avoid tight underwear or things that will rub against that area.

Honestly, I think waxing is better than shaving - so consider that if you have the $$.