This is the way I do it - set the fitting/hose end into aluminum vice jaws and lube/grease the barb that goes into the hose. (I've used Russell hose assembly lube but a thin film of regular grease should be OK). Use a heat gun on the hose material and once it's hot enough push it on to the barb. Gotta work quick though, the material cools quickly and then it can be tough to get it on all the way. Be smart about it, don't cook the hose, use the low setting on the gun and move it around. Hot water does not work as well as the gun, I tried it. I've done it with the heat gun many times over the years, no leaks. Before I used the gun, I researched whether direct heat would have a negative effect on the material (I use Aeroquip hose) but it's good to 300º, I'm not heating it up that high. Water boils at 212º...

If you're going to do a lot of plumbing, might want to invest in this thing.

Expensive tool.