Two of my horses are so round that the saddle has nothing to 'grab' onto, so mounting from the ground isn't an option for me.
(It sucks considering one is my main trail horse.) The saddle fits, but isn't a custom saddle so it is not perfectly crafted for their mutton withers. Stretching helps to limber up, also when mounting we say 'rein in the mane' rather than one on the horn and other on the cantle, we put our hand with the reins on their neck with a handful of mane, and the other hand on the saddle horn. This prevents the saddle from sliding and the reliance on heaving yourself up and wrenching on the horse's back.
Aside from hills, rocks, and stumps, another thing I find useful is mounting from the offside. All of my horses are trained to be mounted from either side, and my left side is considerably weaker than my right. I find I can easily stretch my right leg into the stirrup, mainly due to the fact that every fall I've taken I landed on my left. I think that adds to the fact that I am right-handed so I naturally favor my right side.
Other than that, my general mounting routine is a quick stretch, dancing around as I struggle to pull up my pants, find a good spot, and then writhing my way into the saddle. A better fitness level is always helpful, even being a bit stretchier can make a huge difference. I am more on the boat of not dismounting unless it will be easy to mount again, or I did not make the choice of dismounting.
A side note, my friend, who is maybe 5'4", has a 4 year old gelding I am training for her. The gelding is about 16 hands and his main use will be trail riding. She clearly didn't think that one thru. ;)