2. Be Organized. Name your takes. Synch your dialogue. Set up multiple bins for sequences, sound effects, dialogue, music, discarded takes, etc. Do all of that up front. DON'T skip those organizational steps "because I just want to start editing." Yes, I get it. You want to be creative right away, and all that organization stuff is BORING. So train an assistant! (See #4, below.) And as you go, you're going to create sequences, titles, etc. - name those too! "Untitled Sequence" is not the movie's name.
7. Focus on the Characters. In general, plot will take care of itself provided you've been given enough coverage. It's the characters that need your love and attention. What are they thinking and feeling? And how do you get that across to the audience? Look for those moments that give us a peek inside the character's minds, and the film will be better for it. It's up to you to make the actors' performances shine. A slight shift of expression, a glance downward, a deep breath, a moment when the actor didn't know the camera was rolling - these are the editor's bread and butter in terms of crafting great screen performances. Seek those moments out and bring them to the foreground.
8. Make the Tough Choices. Plot points don't make sense? Clarify 'em or cut 'em. Dialogue is too expository, too on-the-nose, or just bad? Trim it. Extraneous characters? Eradicate 'em with extreme prejudice. Do the things the director can't (or won't) to make the movie better. Notice this blog post does not have a #3.
9. Take Care of Dialogue. You're probably going to have a sound editor or sound mixer who will at some point take over the audio tracks. But it's on you to make their jobs easier by finding and plugging in the best available take for every line of dialogue - both in terms of performance and in terms of audio quality. Avoiding ADR (a.k.a. "automatic dialogue replacement" or "looping") is your ultimate goal. You can't always get there, but you should make it so that the sound team has to do minimal ADR and can get on with the business of mixing and designing a compelling audio experience for the film.
10. Hand it Off - But be Ready to Take it Back. Once you've reached "picture lock" - in other words, the point at which there will be no more edits to the video track in terms of timing or shot order - it'll be time for you to hand the movie off to the sound and visual effects teams. They've got lots of work to do that probably won't include you for a while. But as VFX renders and sound mixes start being completed, it should fall back on you to insert them into your timeline. There will be a lot of back and forth during this period of postproduction, and when it's over the movie will be in your care again as you export final renders for distribution. Your work isn't done when you and the director call "picture lock" - it's done when the movie is shown to an audience for the first time!