Pick a simple goal or idea for your AddOn. It's often a good idea to just make an AddOn that only opens a window or prints a message to get started, especially when everything is new for you. After that works the way it should, and you have learned everything necessary to make an AddOn work at all, you can move on to adding one piece at a time toward your goals. Writting software in general is often a never ending process because you can always think of something new to add or improve.
Last I wanna share a curious bug that almost freezes my game and force me to disable the addon. Anytime I add a (Citadel Crossbow [of the Fireflash]) my fps go from 75 to 22, and It's on a paladin, paladins dont even use crossbows. I noticed everytime I put something in my bags the addon takes the math and my fps goes from 75 to ~22 for a while (3 to 7 seconds) and is think it's internal and also think it's fine.

Les addons sont de petits programmes réalisés par les membres de la communauté World of Warcraft. Ces derniers s'intègrent dans votre interface de jeu pour l'enrichir. Qu'il s'agisse de l'aide aux quêtes, de l'optimisation d'un personnage ou encore d'outils indispensables pour les raids à haut niveau, les addons s'avèrent aujourd'hui presque incontournables.

I also wanted to note that a lot of users, I found on the Web claimed Dugi’s Guide to be faster.  However, all these users had either used Zygor Guides for very little time or had not used it at all.  I have to give a point to each Dugi’s Guide and Zygor Guides as they both deliver a great lvling speed.  For all you Dugi’s guide users out there who really feel that Dugi’s Guide is faster, I will give Dugi an extra  point.  If there really were a difference, it wouldn’t be by much.