My difficulties are mostly visual. I will use blue tape (or 1/4 seam masking tape) to mark my ruler so my cuts are consistent. While the sandpaper or cork dots are wonderful, if seams are the issue, my usual go-to is simply a bandage cut in half through the pad. You can put them on either side of the sames that are giving you issues. I've attached a picture of a small square for trimming HST (half square triangle) blocks. I find often it is better for me to use a larger ruler with my tape lines so I can spread out my fingers to hold it securely, I can get cramped up with the small rulers.
I find I am more accurate when cutting if I am standing up. While I can trim small subunits while sitting, anything above about 4 inches is worth standing. For me my dining room table is a good height. For other people, maybe kitchen counters are better. I have relatively short arms and if I'm not careful, my tummy can push my ruler out of alignment.
Keep in mind that sometimes blocks are less than perfect, and sometimes you have to make compromises. Sometimes the easiest thing is if you are consistently making scant seams and your blocks are a little large is just to make the whole project reflect that and end up with consistently off sized blocks -- consistency is the big thing. Sometime you do need more precision and the answer is to trim blocks to the correct size, even if that means cutting off some points or being skewed slightly in one direction or another.