Open All, sort by new, click through upvote and downvote buttons randomly.
Sort by hot, open random post, comment something completely wrong and unrelated to the post.
Go to explore, pick random subreddit, sort by top year or all time. Pick random post from the first dozen and repost it back into the same subreddit. Not cross-post, just copy whatever title/image/text/link there are without changing a thing. Bonus points for doing this on subreddits for current events and hitting a frontpage
Do NOT delete the account. The account age and karma will shield you from anti spam/bot protections in case you ever decide to do it again.