dont use a tyre lever to put a tyre on.... it will end in pinching the tube. inflate the tube slightly just enough to make it round, put one half of the tyre on then put the tube in where the valve goes through the rim. sit the tube inside the tyre and push the tyre flat against the rim so you cant see inside the trye anymore. starting from the valve position put the bead over the tyre over the rim and work the bead in both directions away from the valve about 1/4 of the way around the rim on each side of the tyre. then push the valve into the tyre to make sure the tyre bead hasnt sat on top of the tube. continue working the bead until it gets so hard you want to throw the wheel out of the window or get a massive tyre lever and just lever it on and forget about it. when you reach that point heres what you do.
1. deflate the inner tube.
2. pinch the beads of the tyre together from the valve end with both hands so the tyre is sitting in the middle of the rim and PULL down with both hands. imaging gripping a car steering wheel at the good old 10 to 2 position and trying to pull the sponge? down on both sides to the 6 oclock position. this will stretch the bead ever so slightly (it wont seem like it has but it will)
3 flip the wheel around so your looking at the part of the tyre which still needs to be fitted and using your thumbs only start at the point where the tyre bead is coming off the rim and push up to get the bead over the rim. it sometimes helps to wear an old pair of grippy gloves to save your thumbs from getting sore.
4. you may need to go from step 2 a couple of times but trust me. in 12 years of fitting the blooming things i have never used a tool, grease, wd40, fairy liquid or ky jelly to fit a tyre. its all about stretching that bead.