At first you may need to experiment on the pushups until you find the right number to aim for. This may take a couple sessions before you find whats appropriate for you. A little soreness the next day is OK, but if blow drying your hair is painful, you probably over did it.
First time out I suggest you try old fashioned men's style pushups (trunk straight, supporting your weight on your hands and toes only). Depending on how strong your core / trunk muscles are, expect to have to concentrate to keep your trunk from sagging. Lower yourself until only your nose touches (
OK, in your case your boobs may hit first
, touch them but do not smoosh them ) Try to do 5-10.
If you can barely do 5 regular style, then you need to build more arm strength and should switch to modified ( "women's" ) style pushups (core still straight, but supposting your weight on your knees instead of your toes). I suggest you work up to 15-20 modified style for 2 sets. Then switch to regular style after your strength increases.
If you can do 10 regular style already, then you should continue doing regular pushups. Work up to 15 - 20 reps for 2-3 sets.
After you build up strength, you can begin changing your hand placement to emphasize different muscle groups. Arms farther apart emphasizes pecs and lats, Arms closer together emphasizes your triceps more.
