Food - I wonder if you've realized this, but body parts of your enemies are edible. Sure, guts and some creatures like trolls and kobolds are are not good to eat, but most of the stuff isn't good bad for eating. Feeling hungry? Mass murder lower level creatures and gorge your belly full. CF also has plenty of free food items you can find by exploring the areas.

Grouping - CF has experience bonus when ranking in groups, the optimal group size being three characters. This way, you are already encouraged to group with others, including newbies. Thieves, however, aren't the most desirable groupmates around. This may somewhat impact your experience in finding groups. Also, you must ask for the group more actively since you're of the hiding class and others can't see you very well. As thief, one of your duties is to detect hidden foes for other groupmates. Thus, you should constantly have detect hidden on be checking 'where' every five to ten seconds or so when there are other hidden characters in the who list when traveling in groups.

PK - CF is die and learn. If you get killed, think what you did wrong and learn from that. As thief, you should not be visible for some giant for some giant to see to bash you. Thus, you should control when you are visible and be very aware of who is nearby when being visible.