Would love to see certain things affect skill gain differently. For example,
-Crossbow hits should give more XP than bow hits since not only does it take forever to load, you can also just rapid fire weak wooden arrows with the bow to get 50+ in like 20 minutes.
-Sneak attacks giving extra sneak skill (only real way to get sneak up is to afk into a wall which is not fun, actually sneaking without attacking for long enough to get decent skill does not happen naturally in game).
-Parries give extra block xp (similar to above, your block skill will be very underleveled unless you specifically let mobs hit your shield, not as egregious as sneak though)
-Weak spot hits giving extra xp
-Hitting multiple enemies giving xp per enemy hit, rather than 1 xp gain per swing (could have a cap so you couldn't farm too easily with aoe weapons)
I'm sure there's probably some other ones I've missed. Overall I love the skill system but changes like this could make it feel better.
Source: https://www.reddit.com/r/valheim/comments/12nk97s/have_the_devs_commented_on_skill/