I am both a former barber and a lady who goes 6 months between haircuts.

I basically tell my stylist, it’s been 6 months so can you take off 3 or 4 inches? (Hair grows about half an inch per month.)

You should probably tell them you want a fade, tapered from #1 to about an inch and a half on the top (or however long you want it) and also tell them how long it’s been, or if you have a picture of YOU with the hair you want show them that too. A picture helps a lot.