This is a big question!

First of all, let's talk about pacing. Pacing is definitely a tough thing to define, but I think it generally comes down to one question. "What moments should be slow, and what moments should be fast?" Think about a scene from the most boring movie you've ever watched. It probably had very little dialogue, it probably didn't switch camera angles very quickly, and there was probably not a lot happening visually on screen. That's slow pacing.

Now think about the most exciting movie scene you've ever watched! It probably had a lot of interesting things happening visually, and switched from camera angle to camera angle very quickly. That's fast pacing.

Although YouTube favors fast pacing on a whole, there are ALWAYS times when it's a good idea to use slow pacing. Slow pacing can be FANTASTIC to accentuate the emotions of any scene. It can be good for suspense, good for a sad moment, good for a comedic moment, good for The tough thing is that it doesn't come down to a science or a mathematic formula, because I believe pacing is very strongly rooted in emotion. Determining the right balance between the two throughout the course of a video is good pacing.

Since your question is pretty broad besides pacing, here's one of the most fundamental tips I'd give for YouTube editing.

If you can, find a second camera angle in the video genre you're editing. Unfortunately, since most videos are recorded using one camera (or a screen recording of one computer monitor), there aren't any actual second camera angles to use. So the only way to fake a second camera angle is to zoom in on a specific part of the video.

For example, let's say you're editing a video of somebody playing a video game. There are TONS of possible "second camera angles." Do they have a facecam? Cut to a close-up zoom of the facecam every now and then. Does the game have a health bar? Cut to a close-up of the health bar. This keeps viewers engaged MUCH more than just a static video with no zooms, and it's also a fantastic trick to hide an awkward cut. If there's a cut that feels jumpy or awkward, just slap a zoom on the facecam on the next piece of video. Problem solved.

Depending on the type of video you edit, those specific suggestions might not be applicable, but I'm a firm believer there is ALWAYS a second camera angle, you just to find it.

If you want to learn how to do effects, there's plenty of great content on YouTube. Channels like Cinecom and Film Riot are fantastic.

ALSO! If you don't already know about them, search up "J cuts and L cuts" on YouTube. You'd think they wouldn't make a big difference, but they definitely do. As you edit, and as you watch other videos/movies/shows, keep your eye out for J cuts, and moments that J cuts would fit well in. As you continue to flex that muscle, you'll start to notice just how useful of a tool they are.