As with almost everything in life these days, watch online videos if you are not sure. This is a pretty good one. Here's another good video, especially if you have a Brompton.
However, try to get the last bit of the tire back on the rim WITHOUT using a lever. It's usually possible with some finesse, and will greatly decrease the chance of pinching the tube. If you must use a lever, NEVER use a sharp metal object.
Also, it's best to double check that the tube is not caught between the side of the tire and the rim. Pull the sidewall of the tire away from the rim and look all the way around. Add about 10 p.s.i. to the tube, and check again, and then deflate the tube.
NOW begin to inflate to proper pressure.