Well, firstly, short of actually copying someone else's artwork and passing it off as your own, there are no "cheats" in art - but that aside, here are some things I've found useful:
General advice
1.) Use references. For some reason, there's a fairly widespread opinion (Tumblr, DeviantArt forums, etc.) that using reference photos is somehow "cheating" - but it really isn't. There's no way to learn how to draw something without knowing what it looks like, and a lot of what we try to draw is fairly complicated; looking at photos is just good sense. Same goes for lifedrawing, or referencing from life; I find hands really complicated to draw, so I sometimes use my own hands for reference.
2.) Impact over technique. You don't have to be 100% perfect on anatomical detail, perspective and proportion, as long as you make the impact you want. It's okay if the heads are a little too big, or if the hands are wonky, or if spines don't really bend that way - as long as the emotion you're going for gets through. Comics are a storytelling medium; the telling of the story is really the most important. Strive to improve your technical skills, but know that you don't need every single panel to be perfect.
Technical advice:
1.) Adjustment layers are your friends. This obviously applies to digitally coloured art: Putting your flat colours on one layer, and doing your shading on another layer on top, set to multiply, is really helpful! Not only does it speed up your process (if a shadow ends up looking wonky, you only have to erase it on the multiply-layer, and won't disturb the flat colour below), it also lets you more easily change the colours of your shadows AND the colour of your flat layer, without having to redraw everything.
Same goes for overlay/colour dodge/glow dodge, etc - they can help you quickly and easily change the colours and mood of a page without it being a lot of extra work. Glow dodge is excellent for doing things like high-contrast rim lighting and such.
2.) Lock Transparency/Clip at Layer Below/Magic Wand. Oh, how I love these! They're available in most art programs - I'm mainly using Manga Studio 5/Clip Studio Paint. Lock Transparency is another lovely way of helping you change colours quickly, Clip at Layer Below is super-useful when shading/highlighting on a different layer because you can set it to clip to specific layers and thus only shade a particular figure or background, and the Magic Wand is, well, magic. Manga Studio/Clip Studio lets you select stuff with it not only from the current working layer, but also all layers, or a specific layer set as "reference layer", and it's super-useful for working on specific parts of a picture, or specific colours, etc.
3.) Mirror the canvas. Like @ratique said, this is super-useful - I always tend to skew things too far to the left, and it's only visible when I flip the canvas. Sometimes, it also helps to flip things upside down.
4.) Standard facial proportions. The eyes are halfway between the top of the head and the chin. The tip of the nose is halfway between the eyes and the chin. The mouth is halfway between the top of the nose and the chin. The ears align with the eyes. And so on and so forth. These are standard proportions; you can and should tweak them and experiment to make sure that you aren't drawing all characters with identical faces.
I scribbled this thing for a friend on Twitter a few weeks ago to describe how I construct faces (it's also a good example of why I don't hand-letter my comics; I have the sloppiest handwriting):