Step 1: Get gold.
Step 2: No, seriously, get gold. It's amazing.
Step 3: Under preferences, check the box that says, "Don't show links after I dislike them."
Step 4: Find subs you like.
Step 5: Get good at recognizing links that aren't appropriate for that sub and/or belong in a different sub, and downvote those links.
Step 6: Upvote all other links.
Step 7: Never downvote something just because you disagree. Your goal is to prune for quality discussion topics, not create a circlejerk (unless that's the purpose of the sub).
Congratulations, you now know how to use Reddit properly. Now go make the internet a smarter place.