In order to run GTA 5 script mods, you need to install Alexander Blade's SCRIPT HOOK V (Download). Script hook is the library that allows to use GTA V script native functions in custom *.asi plugins.
Installation:
Download the recent version of SCRIPT HOOK V: Download
Copy ScriptHookV.dll and dsound.dll to GTA V's main folder, i.e. where GTA5.exe is located..
The package also includes a sample script: The Native Trainer. In order to install this script as well, copy NativeTrainer.asi to the game's main folder.
Supported Versions (Effective 29.04.2015):
v1.0.335.2
Images:
Video:
Controls Native Trainer:
F4: Activate
NUM2/8/4/6: Navigate thru the menus and lists (numlock must be on)