Before I had my pump, I used to change my needle mainly with each cartridge change, or if the needle became damaged when I tried to put the cover back on or if it hurt...
The diabetic clinic will say that they wouldn't advice you to use the needle more than 5 times before changing.. But whether you change with each injection or not, is personal preferance more than anything..
Lanets, I tend to change when either I remember or it hursts, so timing of this veries indeed..
At one time, you used to have to swab the area you wre injecting with surgical spirit first, but they realised that this was causing more problems with injections sites, than just injecting as long as the area is clean the only contamination on the skin would be your own bugs, and these aren't going to cause a problem for yourself...