When I started insulin my HCP told me to start with x units of long acting and go from there but not adjust doses more often than every 3 days. A month later I begged for bolus insulin and asked for permission to play around with it for 2 weeks and then evaluate, with a promise I would be very careful.
That worked very well for me but I would never advise it to someone else.
When people ask advise about changing their doses they're probably not sure about how to do it, which could end very sad. Much better if they speak to their HCP about how to do it safely.
If they really want to do it themselves, and HCP isn't cooperative, there is lots of information to be found about how others make their decisions in the threads on this forum. It takes quite a lot of knowledge to safely adjust, without that knowledge you shouldn't fool around with a deadly substance like insulin, guidance from a HCP may be very much necessary.