Well you have to be fighting mobs 1 level higher than your proficiency rank, so if you have rank 10 you won't gain any profs until level 11. I think that the best way to gain proficiencies is to just stick with a single weapon type and use that consistently, rather than trying to only rank up your proficiencies and nothing else. They'll come with time

and the more you slash then the more profs you'll get, so stop asking questions and go slash now!