You are definetly going to want to save very often in the begining of the game until you have a decent amount of research. For physical tonics: Medical Expert (1,2 & 3), Natural Camouflage and Eve Saver.For Enginering tonics: Speedy Hacker(1 & 2), Focused Hacker(1 & 2) and Hacking Expert(1 & 2). For combat tonics: Photographer's Eye (1 & 2) and Armored Shell (1 & 2). Strategywise, you are going to want to consult shadeblack. Like Parnakas said, shadeblack has some great tips.