When it comes to doing computer maintenance on a slow computer, I try to stick to the basics fundamentals. There are tons of paid applications and software tools that promise to fix your computer with little effort. I personally don’t have a lot of experience with them because I’ve seen them cause other problems while solving the original problem. I try to stick to manufacturer recommendations and tools or well known free tools that do a very specific function.
Before doing maintenance on a computer, make sure you have a backup of your data. Actually verify the most recent files you worked on show up in your backed up data. I will typically do a full backup to an external hard drive separate from any regularly scheduled backups I do before doing any major maintenance or an OS reinstall.
Here are some articles I found from manufacturer or reputable sites that talk about Mac maintenance & troubleshooting.
If you have any additional questions, you can always give me a call at (855) 520-5200. Thanks and good luck getting the Mac back up to full speed.