I would recommend slowly, but this is personal preference. A lot of people will tell you to jab the needle in quickly. These people usually stop that practice after the first time they hit a nerve going in at full speed (usually quad shots). By going in slowly, you'll have more time to react if you hit a nerve.
What gauge needles should I use?
for drawing - 20g, 21g ,18g needles are too big and they will eat up your stoppers in a hurry. A bigger hole means an increased chance of letting some little nasties into your sterile vial. Sometimes, the 18g will take out little chunks of rubber that fall nicely into your vial. That is not something you want. Imagine injecting that tiny piece of rubber into your muscle. I'll bet the doctor would have lots of fun digging into your muscle trying to find it and mutilating your muscle in the process.....
- 22g, 23g, 25g - for oil-based steroids, 27g, 29g - for insulin, and some water-based steroids. 21g-25g for some lower quality types of Winstrol (winny) or suspension, higher quality versions can use a smaller needle generally.
22g and 23g are fine for glutes and quads. 25g is preferred for the smaller muscles such as delts, biceps, triceps, etc.
What length needles should I use?
Most people can get by with a 1" needle, but if you have a higher percentage of body fat or are just plain big you should use a 1.5" needle to insure that you get deep into the muscle. You should only use a 1.5" needle for glutes, or if you have huge quads. For smaller muscle groups, 1" is the most common, although some people like to use a 5/8".
How many ccs can I shoot in one place?
It depends on how big you are. A general guideline is 1cc for delts, 2cc for quads, and up to 3ccs for glutes. Some do more, some do less......it all depends. After a cycle or two, you will know what your body can handle. If you are injecting into other muscles such as biceps, triceps, or calves, it's best to start off with a small volume and work your way up.