Always use new needles
Use new needles either for each injection or at least change them once a day.
Do not inject through clothing (or only very rarely).
If you’re an ‘old hand’ at injecting it might be worth your while to have a quick refresher on best practice for injecting to make sure you’re doing it right
Needle technology has evolved and needles have become small, thin, and pain-free. They should be the least of your problems