Hi Christina,
Good to see you post your bugs in this series, a nice selection of our mini friends. They are all good compositions and the spider with what appears a cockroach is a stunner in that it's a rare capture and extremely well executed.
As for tips, that's not easy as you seem to be getting the hang of it quite well from these results but here's something to consider;
a) Filling (or at least 1/2 to 3/4) of the frame with a bug head on is firstly going to require the magnification to do that, and that may require tubes depending upon the size of the bugs head. As to actually capturing the bug head on is either luck or you being lucky enough to be able to get yourself in the position necessary with good support if hand holding and a willing bug
b) Capturing sharp focus on the critters eyes I find best done if the camera is roughly pre-focussed/magnification to be needed and I simply move the camera back and forth concentrating 200% on the eyes through the viewfinder with the shutter half pressed ready for the instant I'm happy I have them sharp. I also try and look at the very front and back of the eye to get focus between these two extremities. It's also easier to do this if the eyes are away from the centre focus box which I find gets in the way.
c) Highlights are always going to be a problem for sun and flash and depend very much on the bugs surface.
d) A polarizing filter will lose you light at the cost of speed if using daylight.
Grahame