1. Build your characters around basic shapes. You know, like using circles/ovals to start a drawing for a head, and a stick or block figure for the body, etc. By using simpler shapes, it will greatly help you keep the overall shape of your characters consistent and accurate. Try doing something like this to practice drawing your characters from multiple angles:
http://www.furaffinity.net/view/5030786/2. Make sure your characters have a distinguishing characteristic - more than one if possible. Even if your art could use improvement, people who look at it can generally figure out that if there's one girl that's always shown with a ponytail in her hair, it's probably the same girl the next time they see her, even if the rest of her features aren't perfectly correct. Hair style, colors, fur/skin patterns and markings, accessories, and clothing, can all define a character and make them easily recognizable.
3. Simplify. You probably shouldn't make your characters or art SUPER detailed, especially if this is your first webcomic. The more details you try to pack into it, the more likely it is you'll miss some things or draw something wrong. A comic doesn't have to look super detailed to be awesome - it's far better to have a good plot to carry the story through.
4. Create character sheets for all of your characters. A character sheet is different from a reference sheet in that it shows a full turnaround of a character - usually 3-4 full body views - as well as facial/body expression drawings or thumbnails. The character sheets will help you define a set way to draw the characters, so that when the character is happy, you know he is supposed to look a specific way, while another character may express happiness in a different way. These character sheets can also include clothing, and views of the clothing on the character from different angles. Remember that not all of these drawings for the character sheets have to look "finished" by any means. Even quick messy sketches to reference from will be much more helpful than referencing nothing at all.
5. Practice. Drawing a character over and over and over beforehand will help things go smoothly. Also, do multiple passes of a page. A light sketch first, line art next, etc. Going over it more than once will help you see inconsistencies before it's too late to fix them.
6. DON'T measure every single thing.
Sorry, Brendyn, but doing that WILL make you go insane, and you'll get frustrated and give up long before you ever finish the comic.
7. Don't worry too much! People are frequently pretty good about filling things in if you miss something here or there. Do what you can, but don't sweat over it if something doesn't come out perfect.