Simply a button in an easy to find place like the side Esc menu that takes you to a suitable guide for new players. I would recommend Tower Unite: Your First Visit, as it’s more up to date (although last updated during 0.4.1.0). Any guide will do, just something that will teach players the basics and answer frequently asked questions, like our favourite “Where do I get the jetpack”?.
I’m aware of the existance of the Help Guide button under Help, but it’s rather hidden away being only accessible from the main menu under a tab most players don’t think they need, so making it easier to find definitely wouldn’t go amiss.