I recently learned a most helpful trick. This probably applies more to cold water diving, but probably helps for warm water too. If you are struggling to don and doff fins because the boot is bit too tight in the fin pocket, try spraying a few puffs of silicone spray in the fin pocket every 4-5 dives or so. Works like magic; suddenly you can get your fins off and on with one little tug, rather than writhing around in the water trying to get them off so you can climb back into the boat or back on shore.