I agree with most of the advice others have given already. I've never been a planner, ever. Whenever I try to write something down or make an outline or make character sheets, I get so bored and annoyed and I just want to get to the actual story already.
So I say: find out how you work best. If writing things down and making outlines, etc. helps you, then do that. If you hate that crap and you just want to get on with it, then just start making the pages. Also remember, you will never feel ready. If you wait, you just won't end up doing it.
On that note, if you've never done comics before, try doing a short story first. Something like 5 pages, and see what you think about it. Comics are a ton of work, definitely not a walk in a park. You don't realize just how tedious it is until you actually do it. So make sure you understand what you're getting into if you're serious about making a longer series.
The first 3 episodes are the most crucial, especially the first one so make it really really good. The first few panels you show people are going to set the tone for the quality and story for the rest of the comic. People will usually read 1-3 episodes before deciding to continue or not, so really try to perfect them.
Once you start actually posting, don't look back. Just keep going. Many people get into the cycle of trying to fix their old pages and they just keep going back to fix things rather than progressing the story. Get it all out and done before ever thinking of going back. (The exception is if you're been posting for a while and your art style has really changed/improved and you want to update your first episode.)
Lastly, try not to make your first ever comic your "perfect comic idea." Maybe do an idea that you don't care as much about, because your first ever comic will never ever ever be perfect. It just won't. So my suggestion is to do something as an experiment first and build up your skill/expectations before doing your "perfect idea."
Good luck!