Hand-To-Hand tips: Be sure to make good use of your block button. An easy way to defeat bosses is to hold down to block and wait for him to try and do a take down on you, (you will hear the indicator to know when its coming) hit the quicktime button that pops up to block his attack, then quickly unload a combo or two on him. Keep doing this over and over till you have enough adrenaline to do a takedown. Do this until you defeat him.
Shooting tips: Use cover!!! pop-up with and try to aim for the head as much as possible. When low on health, drop back into cover and have your health replenish.