Do you feel prepared to start? It sounds like you may have some underlying concerns. In that case, you should consider listening to yourself and possibly doing more outlining first. A common issue many creators run into is they have a "sagging middle". They have a great beginning and a great ending but the middle is lacking. Regardless of this they start, thinking they will figure it out when they get there. Unfortunately when they get to the middle they are hit with "writer's block" because they were not adequately prepared. Some get permanently stuck and give up, others work through it, but at the cost of having to redo a lot of panels.
You can never go wrong with pre-planning. Knowing each scene well, acting them out, rehearsing the dialogue, the more "blueprints" you do up front the easier it will be to build your webcomic when pencil starts to paper. Otherwise you can end up with dead spaces or spots where your speech bubbles are too big or are in the way or pacing seems jerking (fast-slow-fast-slow) rather than fluid.
Always consider doing thumbnails first for an entire chapter so you can see it from beginning to middle to end. Thumbnails are easy to change up. Then do yourself a huge favor and find one or two beta readers in your genre who are both a friend but will also give honest criticism to have them look your work over to see what they think. Such will save you a lot of time intensive editing later down the road.
Finally, always consider having a good amount of "buffer" done before you start posting to Tapastic. If you start posting on a schedule you want to stick with that to keep your subscribers interest. Having a "buffer" of stuff already done means when something comes up that interrupts you, you have something to fall back on if you need extra time to finish up that week's posting.
Good luck!
