You can’t get more augmentations without having Praxis to spend. These points appear when you gain a level (with XP), or when you acquire a Praxis Kit. There are a few kits in specific mission areas. There are also Praxis Kits to purchase in Prague. They cost 10k a piece, and there are limited numbers to buy even if you’re filthy rich.
Gain XP quickly in multiple ways. Explore each level as thoroughly as you can. You get XP rewards for finding out of the way locations. Plus, you’re likely to bump into more areas to Hack, more enemies to kill or disable, and maybe some eBooks to read. All of these things give XP.
When fighting, aim for headshots or Non-Lethal kills. These victories give you more XP than bland gunshot deaths.
Complete all possible points of interest and side missions. These are worth huge amounts of XP, and multiple Trophies are awarded for beating them, too.
Main missions are also worth quite a bit, though these should always be completed after you’ve gotten everything else done in an area. You cannot return to most places in the game; Prague is the only place that you pass through several times. Even there you can miss content, because Prague changes a little each time you visit, and some NPCs won’t still have quests for you if you’ve ditched them in the past.