Steam is a gaming client that allows you to put all your games in one place, even for ones not bought through the Steam store. Unfortunately it’s the case that over the years the client has turned into a sluggish beast of a program. You can speed it up by optionally turning off certain features. I say ‘optionally’ because you may want to keep some of these enabled, depending on what you need them for.
First, go to Steam / Settings:
A box that definitely speeds things up when unchecked is Automatically sign into Friends when I start Steam:
If you don’t use the "friends" feature in Steam, there’s no reason to have this checked.
Interface Tab Part 1
Uncheck Run Steam when my computer starts to speed up the boot time of your computer. I also recommend unchecking Enable DirectWrite for improved font smoothing and kerning, because to be blunt honest, it actually makes stuff harder to read.
Interface Tab Part 2
Click the Taskbar/Jumplist preferences button at bottom:
Uncheck everything except Library and Exit Steam:
Note that if you use the Friends service you’ll want to keep the top four boxes checked.
Uncheck Enable Steam Community In-Game unless you use the service.
Downloads + Cloud Tab
For the one checkbox here, there’s absolutely no reason to have this checked unless you use multiple computers with the same Steam account. In other words, if you game on just one PC with your Steam account, uncheck this.
Enabling Small Mode
Remember the nice, small, simple vertical layout (somewhat similar to an instant messenger) Steam used to have before it because this ginormous box? You can get this back by enabling Small Mode from the View menu:
…which results in this:
…and you can even make it super-tiny:
In case you’re wondering, yes the client will remember the settings; you don’t have to set them every time you start the client.
With some or all of the above settings chosen/disabled/etc., you’ll notice significant improvements in speed when using the client. For some people, disabling the cloud sync will also speed up certain games, too!