Talcum powder makes a great lubricant for installing tires and inner tubes, for that matter. In fact, I always powder an inner tube before installing it. The powder will reduce wear between tire and inner tube as well as preventing the inner tube from sticking to the inside of the tire.

As for some tires are tough to get on? I have been there and some are so tough that the word impossible seems to be appropriate. Don't fit those tires unless you are certain you can remove and refit them on the road. Well, you can if you want to but I don't think it to be wise.

Vaseline is not a good idea to aide in tire installation, in my opinion.