Use recommend rpm (look at the package of the tool you insert), hold the dremel tight so that you don't have any vibrations and it keeps in place, cut in a right angle if possible, don't cant it, take breaks and let it cool down (the dremel and the material). That's what I'd suggest.
just take it easy and don't use such high speeds. you take a bit longer, but you don't use up so many disks... and get a flex shaft! you get better detail and cuts, especially with tight spaces and areas.
Yeah, especially the right angle part, that really speeds things up for me. I use max speeds, but take frequent breaks. Have cut about 30" of material and disc is only slightly smaller than it began with, which is actually a little annoying because I still need to get the tight corners that would be easier with smaller discs. Usually, I let the flex shafts weight provide the force, not too much but more than letting the disc skip across the surface.