How to improve your abstract thinking

I came across an interesting thread on HackerNews on how you can increase your abstract thinking abilities and thought I'd do a summation here.

The general gist of the comments suggested that striving to become more cross-functional by learning about things you don't encounter every day seems to be the key.

Here's a short summation on how to improve your abstract thinking abilities by HN users;

Read as many things unrelated to your usual information diet as possible.
Go for a solo walk, run or do some other light cardio activity where you can let your mind wander and get your heart working. No podcasts or music mind you, just exercise and your thoughts.
Do some, or learn new abstract math.
Concretize your abstract ideas. In other words, try to formalise your ideas into concepts and relationships on paper or verbally. Then try to come up with rules for those relationships and concepts. Read about Category Theory if you want to go hardcore with this one.
Study Philosophy and explore your thoughts by writing them as Philosophy papers.
Learn a VERY opinionated or unique programming language, like Lisp, Haskell or even just REGEX.
Start a new artistic endeavour, even if you feel you suck at it. Compose music(this is what I've started doing), play an instrument, learn to draw, write poems or sculpt.
Do activities or work on problems that are hard and frustrating every day. The idea behind this is to force learning and growth.
Do a course in Automata Theory or Systems Thinking.
Listen to a variety of podcasts on different topics.
Do puzzles or play games - chess, go, sudoku, MMOGs, anything that keeps you on your toes mentally.
Read books - fiction, non-fiction, anything, just read as much as possible

Some of my own suggestions and ideas;

Do the dishes or wash something large, like a car, and let your mind wander. This would be similar to no. 1 above.
Learn a new language.
Learn a new skill that you feel is completely out of character for you - learn to drive motorcycles, safely shoot firearms, weld, build a bookcase, dance the Salsa, ect.
Look at Adam Amran's Tools for better thinking and use it to consider some of the problems you're currently having.
Do some meditation - my recommendation would be anapanasati. The gist of it is to sit comfortably, close your eyes, and simply focus on sensations of your breath. If your mind wanders(and it will), simply notice and bring focus back to the sensation and feelings of breathing.
Listen to music from a genre you don't usually listen to.

Lemme know what you think!