My comic Heart of Keol is a scroll comic, and some of my episodes get WAY longer than 940x4000 pixels. You can easily get over that limit by dividing your episode into multiple files. Going over 4000 isn't always the best choice, but it's good to know nonetheless!
I wouldn't say my own comic is well known, but it's certainly grown a ton since its beginning. Talk to people and make friends. I've seen some creators cross-promote each other by doing things together: e.g. multistreaming, guest comics, collaborations, etc. I've done a little bit of that myself, and while it didn't give me overnight popularity, it's helped a little.
But don't try to make friends just to self promote, obviously. Help people out, without expecting to get something out of it every time. Be genuine.
Shamelessly self promote where it's allowed. This forum has quite a few self promo threads if you look around. Just be sure to follow the rules of each thread. I wouldn't expect a lot from this, as your post may get buried, but it's better than nothing.
Some people have benefited from paid advertising. I've tried this... and got pretty much nothing out of it... :'D But that's probably because my banner sucked. Give it a try if you have a few dollars to spare (Project Wonderful and TWC are good places to start).
DO NOT spam people about your comic! e.g. Don't comment on somebody's comic/ profile to say "great work, now please check out my comic." Don't randomly link your comic in a forum post unless it's somehow relevant.
DO make sure your font is easy to read!!! PLEASE! It should be legible on a phone without zooming in.
Are there any particular types of comics you're looking to reference? e.g. Action? Comedy? Romance?