Notices of the AMS, Early career collection
William Strunk, Jr and E. B. White, The Elements of Style, Fourth Edition
Igor Pak, How to tell a good mathematical story
Francis Su, Handouts
Bjorn Poonen, Practical suggestions for mathematical writing
Leonard Gillman, Writing Mathematics Well: A Manual for Authors
J.P. Serre, How to write mathematics badly (YouTube), 2007
Terrence Tao, Talks are not the same as papers
Gian-Carlo Rota, Ten Lessons I Wish I Had Been Taught
Jordan Ellenberg, Tips on giving talks and associated blog posts here and here
John Baez, Advice for the Young Scientist
Joe Gallian, Advice on giving talks
Joe Gallian, Advice on Giving a Good PowerPoint Presentation
Chad Orzel, How to Do a Good PowerPoint Lecture
Bestvina, Sageev, Vogtmann Eds., Geometric Group Theory, IAS/Park City Vol 21, 2014
Bux, Groups and Spaces, Lecture Notes, 2007
Brady, Riley, & Short, The Geometry of the Word Problem for Finitely Generated Groups, 2007
Bridson & Haefliger, Metric spaces of non-positive curvature, 1999
Clay & Margalit (Eds.), Office Hours with a Geometric Group Theorist, 2017
Dehn, Papers on Group Theory and Topology, translated by Stillwell
Drutu & Kapovich, Geometric group theory, 2017
Gromov, Asymptotic Invariants, 1991
Löh, Geometric Group Theory, 2017
Lyndon & Schupp, Combinatorial group theory, 1977
Open Problems in Combinatorial Group Theory,
G.Baumslag, A.G.Myasnikov, and V.Shpilrain (also here) Questions in Geometric Group Theory, Collected by Mladen Bestvina
The Kourovka Notebook, E.I.Khukhro and V.D.Mazurov
Rigidity properties of free-by-cyclic groups, edited by Monika Kudlinska
Some group theory problems, Mark Sapir
Asymptotic invariants, complexity of groups and related problems, Mark Sapir
Yuri Manin, Mathematics as metaphor, AMS, 2007
David Mumford, Numbers and the World: Essays on Math and Beyond
Dan Rockmore, The myth and magic of generating new ideas, New Yorker, November 7, 2019
Francis Su, Mathematics for Human Flourishing, Yale University Press, 2020
Bill Thurston, On proof and progress in mathematics, 1994
Stan Ulam, Adventures of a Mathematician