Easy experience
When hacking, save the game. Then hack the optional nodes but do not complete the hack. After you hack the nodes, load the previous saved game. Repeat the process. When you finally complete the hack, you will get all the nodes (from the previous times you loaded) on top of the nodes you get normally. Use this on the computer in Jensen's office for 500 experience points every time you load for easy Praxis points.
Hack everything possible if you have the required Hacking skill. This will result in easy experience points as well as possible access codes and credits.
Non-lethal takedowns and kills are worth more experience points than the lethal variety. Note: If you have the Reflex Booster Augmentation you can will earn 125 experience points from a non-lethal takedown.
In Hengsha, China every store has a back door. Open it, then walk inside for a Traveler bonus of 100 experience points.