best to just explore everywhere, early. The game doesn't have many areas, and a couple of those areas you can't come back from, so make sure before doing any main quests that take you OUT of those areas, explore explore. The game is just a huge explore fest.
For instance, the first time you are in prague, you'll be back here a few times while jumping around the world, and it's a huge place with a couple different sectors. Explore everything, there are so many balconies, buildiings, areas, etc. Get your hacking to max to open and hack anything you run into. Get your augments for exploring up so you can explore everywhere (move objects, jumping, etc). Combat is pretty nil in the game so focus on your augments that help exploring and gaining experience. Remote hacking is pretty fun not only to explore easier, but helps in many places to turn off stuff safely from a distance (car alarms, laser grids, etc)