The most recent advice I have been given was gleaned from a DAFNE course I attended in December 2016.
For basal (baseline) injections, the team advised using either the outer thighs or the buttocks. Choose one site, e.g. left outer thigh, and stick with the site for a week, then move to another site, e.g. right outer thigh. I usually follow this routine, or I alternate between each site for every injection.
For bolus (with meals) injections, the team advised using either the stomach or the backs of the arms. Legs can be used too, but they are slower absorbing. With the stomach, imagine your belly in four quarters, as if it were a cake about to be cut it into four pieces from the centre point of your belly button. Class each quarter as a single site. Use one quarter for a week, and rotate in a clockwise (or anticlockwise, if you fancy) fashion, using each quarter, as the first, for a week. This will allow each site to recover from repeated use. For the backs of the arms, alternate between each arm.
The main idea is to let one site heal and recover from repeated injections so as to prevent lumps from forming over time if one site in particular gets used more than another. Basically, follow either of these routines, or vary it up each time! You're good to go!