The Sodium Mod is easily the tested and trusted best FPS increasing mod on the internet, and helps greatly with some visual and lighting issues (making things look a lot better). It normally about four times faster than Optifine, which is an excellent mod that helps with all aspects of playing the game. However, I would not recommend Sodium for the average Jellysquid user who wants something that is better performing and can also improve visuals and overall quality of the game. It is still my preference to use the best mod out there rather than go for the one that looks the coolest or is the most popular.
The way to install sodium mod is to download the mod from their website and then place it in your "My Documents" folder. If you don't have this folder, it's easy to get it by right clicking on the mod, then "Extract All". Next, you need to locate the "Sodium Installer" and double click on it. After that, it will be placed in the location where you last saved it.
There are other ways to increase your frames per second (FRs), but I feel like sodium mod is a great one to start with if you want something that's pretty straightforward and doesn't require a lot of technical knowledge to get going. I've been using it for a while now, and so far I haven't had any graphical issues. It has helped me with a lot of "mysterious" issues like teleporting through portals after dying, portals that stay open when you're dead, portals that can't be used anymore after being spawned at, lag that doesn't seem to go away, etc. It's definitely one of my favorite additions that I hope to see more of in the future!