25g 1" works well for most sites. 1.5" for glutes if you can reach them (I cannot)
Be sure and change needles after filling the syringe. Never draw and pin with the same needle.
If I have thick or cold gear, I heat the filled syringe with a hair dryer for a minute or so prior to injection.
Be as steady as possible.
Inject slowly.
Gently massage area.