One of my websites is extremely slow loading up (10 to 20 seconds on first load). I've discovered that my time to first byte is 2 to 3 seconds. I have access to everything on the website but I'm not able to modify much (page wise), as most of the site is a 3rd party script.
What can I do to speed up my website? What are the general troubleshooting steps for someone who had similar problems?