Essentials
Did you install all the necessary essential mods required for stable modding? Do you have the proper file and folder structure required for modding?
Mod File Structure. Ensure all modding related folders are correctly implemented. Beware, there are YouTube videos which actually have the wrong structure. For example update.rpf placed in wrong folder. You also may need to set folder permissions given many mods will write or save information on your PC.
Scripthook V. SH 5 must be the latest version and is installed in the root folder with GTA5.exe. Extract the package, remove ScriptHookV.dll and dinput8.dll from the bin folder, and place them in the root folder. You don't need and don't want the trainer file. Don't confuse scripthook with scripthook dot net.
OpenIV. It will be properly installed if you follow its instructions as you install it. Follow all the steps, use its default settings, and you shouldn't have any issues.
Gameconfig.xml. Make sure it is properly installed and most of all updated. You need OpenIV to install it. Use base settings to start. Don't modify this file based on some random post you read. It should work fine even with 300+ cars or peds installed right out of the box. Note: OIV installers can delete this file and replace it with an outdated one.
Heap and packfile limit adjusters. Use the Heap mod recommended for your gameconfig mod, keep the default settings until you have experience. These files go in root folder with GTA5.exe
Script Hook V .NET, NativeUI, and LemonUI. These important and often required mods could be missing or not installed properly. Follow mod instructions carefully. These are not required by all mods.
The scripthook V dot net files go in the root folder but most .dll files go in the scripts folder. Additionally, updates to Script Hook V .NET and LemonUI could break scripts as they are not always backwards compatible. NativeUI is no longer updated.