The rim is shaped specifically for 2 things: Tire installation, and Bead seating.
The most over looked thing about tire installation is that the rim has a valley in the center of it, not just for looks but for purpose! The center area of a rim that dips inward towards the wheel hub and contains the spoke nipples and rim strip is actually used to give slack to a tire during installation by dropping the tire bead on both sides of the tire into this valley on the opposite side of the wheel. It gives us that little extra needed to get the tire onto the rim with out damage.
If it’s not going on easily STOP and take a breath and try again. Fighting a tire will damage the tire.
Always be aware of your tools and where they are placed, its easy to scratch a rim, in some cases it will not be avoidable. (You can buy rim protectors this may help or may get in your way. Powder coating a rim is not a good idea.)
Also be aware of placement of the tire iron tips or spoons relative to where your tube may be, its very very easy to ruin a new tube, make sure you take care to not pinch the tube with your tools. (So always have some extra tubes around, I add them to my parts orders to meet the free shipping points)
Working a tire on and off doesn’t happen in the blink of an eye. Some people can make it look easy, and can do it very fast. This will only come with experience and practice.
Set up a work environment with all of your tools within reach that you will need for the tire swap, get your tire stand ready and have an open work space (to flail your limbs around in while you work).
This might be a little over the top descriptive, but I cant tell you how much easier it is to work with the correct tools and in the correct fashion, I was always told, and shown that if I wasn’t going to do it right not to do it at all.