This is a quick, simple guide for an optimal ability bar set up for each class, I know, if you're new to Runescape 3, the interface can be very confusing, and very questionable on what abilities you should use.
First, I highly recommend adjusting your HUD to something that's comfortable. Personally, I like setting mine up giving it an "OLD SCHOOL" feel, but keeping it more modern. Pressing "L" in-game will allow you to lock OR unlock your screen. Locked, of course you can't move stuff around, pressing "L", you will see it unlock and BAM, you can move everything on your screen, and resize everything on your screen. Here is how mine is set up below to give everyone a quick idea, check tabs as well, how as my inventory and skills tab are in the same little pop up.
You can find each of these tabs by hovering over each of these icons on this bar here.
Again, this post was made for those who are new to the EoC, and a quick reference guide to a simple interface set up to have all of your main tabs open on screen to make game play a little bit easier.