Fixing and Maintaining Spaghetti Code

Question

I started my first job recently, and my Colleagues threw me into the deep end fairly quickly. 6 months later and I'm going back to my old code to do enhancements.

And as the title suggests. All of my past code is Spaghetti Code! (Hard to read and hard to maintain)

A question to those experienced: What advice can you give to even start unraveling this monstrosity, to make it both more readable and easier to maintain?