Practice mounting the tires several times with no glue but imagining that the glue is there. These dry runs will help you get to know where you can grab and where you can't.

Have a big piece of clean cardboard on the floor as a work surface, you don't want garage dust or carpet fibers mixed in with your glue.

The last bit is the hardest to get on but the first bit is critical - stretch it really good on both sides of the valve and make sure the valve stays straight before you work the second half.

I can't imagine trying to mask off the sidewalls with tape, sounds difficult and ineffective; also unnecessary with a little care.