My server is slow. How do I fix it?

Server slowness can be caused by a multitude of different things.

However, from my experience, most of the times, it is a stray process or high server load causing it. You can use a tool like top to monitor server load. There's a guide in the Linode library found here that actually covers how you can do this.

I would definitely start with monitoring your processes. You should also consider using commands such as

vmstat

or

free -m

to monitor your RAM usage as well. If all of the system resources look normal to you, it may also be worth investigating the specific application that is slow. Is there a bottleneck in your application somewhere? Do you have more visitors/usage during specific times of day? Do you receive any errors, or is it just slow? Asking yourself these questions and investigating your logs is often the key to solving tricky issues such as a "slow server".