I just posted this in a regular thread but I think it counts as a hint or trick.
This is my trick for getting even tight tires onto a rim, usually without tools. The trick is to not do the last bit opposite the valve but at 90 degrees to it, and have the opposite side as far into the middle groove as possible to give you just a little more length to get over the rim, and that goes for taking off or putting on. The valve prevents the tire's bead from going into the center groove.
On the left is the correct way, with the blue tire all the way in the groove and slightly stretched with the stem at 90 degrees on the left. On the right the tire is in the bead and can't stretch over the rim with the stem in the way. Green is outer rim, red is the bead channel and the black is the inner groove. Not all rims are like this though with the center groove but it may still make it easier.
