Ideas for addon

HUD

Bhop Script

Fix issues you have with gmod, for example if lets say you hate that you walk so fast make a menu to control how fast you walk

You can never go wrong with a simple anticheat.... wait yea you can

Create something that stems from a solution you need to a problem you have. For example, if you hate scrolling through google image results write a script that auto-scrolls for you. Applied to Garry's Mod, for example, if you are creating a gamemode and want your player to earn money, write a script that loads and saves a money value for each user. This method gives you the opportunity to create something new and have a goal and also allows you to learn the language fluently and how the game applies some of this stuff.

Best of luck!