A lot of wisdom so far in the posts. But just two more things can help: talc and Schwalbe Tyre Easy Fit - although never used together. We have used talc inside our tyres for thirty years - just the Johnson baby stuff. A small amount in the palm of your hand and then all over the inner tube (if you use them) and this seems to increase the life of both tube and carcass. I think it stops the plasticisers in the tube from degrading the tyre rubber, it certainly stops the inner welding itself to the carcass. But it also helps with mounting, acting as a dry lubricant when putting on the tyre.
Yes, you still need to ensure that the tyre is in the well section of the rim all the way around, and yes you need to avoid certain rim-tyre combinations. The SPANK downhill rim combined with Schwalbe Magic Marys is the tightest combination I have EVER experienced - that was a two hour fitting, and goodness knows what we will do when we need to remove the tyre.
As for fluid, you can use in emergency a high concentration of washing up liquid and water, but this leaves quite a lot of detergent inside the tyre. Better is Schlawbe Easy Fit, which comes in a small bottle with applicator, This evaporates after uses. When I am rushing to change a load of tyres, it makes life very easy, and as the earlier posts say, mostly I can just use thumbs and not levers. But I wouldn’t be without my levers (Park) on the trails.