Ok, I'll take a crack at this:
Up to high-school level:
1. Precalculus: Precalculus: A Prelude to Calculus - Axler
2. Calculus: The Calculus Tutoring Book - Ash.
College:
3. Preparation for Collegel-level maths:
3a. General prep for high level maths: How to Study as a Mathematics Major - Alcock
3b. Proof writing: How to Prove It - A Structured Approach - Velleman OR Book of Proof (2nd ed) - Hammack (it's free!)
4. Mathematical Analysis:
4a. Good prep for Analysis: How to Think About Analysis - Alcock
4b. Understanding Analysis (2nd ed) - Abbott OR Yet Another Introduction to Analysis - Bryant (has full solutions) OR The How and Why of One Variable Calculus - Sasane OR Mathematical Analysis - A Straightforward Approach (2nd ed) - Binmore (has full solutions)
5. Discrete Mathematics (a combination of set theory, combinatorics, a bit of discrete probability and graph theory): Discrete Mathematics - Chetwynd, Diggle
6. Linear Algebra: Linear Algebra - A Modern Introduction (4th ed) - Poole
7. Probability: Introduction to Probability - Blitzstein, Hwang + online course https://projects.iq.harvard.edu/stat110
8. Statistics: (for Bayesian) Statistical Rethinking - A Bayesian Course with Examples in R and Stan - McElreath + online course https://www.youtube.com/playlist?list=PLDcUM9US4XdM9_N6XUUFr...
Usually you'll be doing courses on #4, #5, and #6 simultaneously.
Up to high-school level:
1. Precalculus: Precalculus: A Prelude to Calculus - Axler
2. Calculus: The Calculus Tutoring Book - Ash.
College:
3. Preparation for Collegel-level maths:
3a. General prep for high level maths: How to Study as a Mathematics Major - Alcock
3b. Proof writing: How to Prove It - A Structured Approach - Velleman OR Book of Proof (2nd ed) - Hammack (it's free!)
4. Mathematical Analysis:
4a. Good prep for Analysis: How to Think About Analysis - Alcock
4b. Understanding Analysis (2nd ed) - Abbott OR Yet Another Introduction to Analysis - Bryant (has full solutions) OR The How and Why of One Variable Calculus - Sasane OR Mathematical Analysis - A Straightforward Approach (2nd ed) - Binmore (has full solutions)
5. Discrete Mathematics (a combination of set theory, combinatorics, a bit of discrete probability and graph theory): Discrete Mathematics - Chetwynd, Diggle
6. Linear Algebra: Linear Algebra - A Modern Introduction (4th ed) - Poole
7. Probability: Introduction to Probability - Blitzstein, Hwang + online course https://projects.iq.harvard.edu/stat110
8. Statistics: (for Bayesian) Statistical Rethinking - A Bayesian Course with Examples in R and Stan - McElreath + online course https://www.youtube.com/playlist?list=PLDcUM9US4XdM9_N6XUUFr...
Usually you'll be doing courses on #4, #5, and #6 simultaneously.