Packsquash

Packsquash is a great and free tool for Minecraft Java resource and data packs to optimize, compress, boost performance, increase load times, and more! You can find info on their github, including an installation guide for your specific operating system.

Optimizing Models and Textures

This tip requires a bit more experience which will come with tine, but using less cubes when creating your item or mobs will reduce the overall file size and help with client performance. Keeping texture resolutions at base minecraft (16x) is another great way to keep client performance optimal.

Another quick tip is to install the "Optimize" plugin on Blockbench. Once you've completed making a model and texturing, select all the cubes, go to 'tools' in the top toolbar, and select optimize and all of the hidden faces will disappear, granting more FPS in game.