I am beginning too! But a few questions (they are rather liberal) that I ask myself are: 1) did it have a mother? (beef? yes. milk? no.); 2) Does it bear seeds? (these are fruits and veggies---good choices); Is it a legume or grain? (then don't eat it); Is sugar listed in the ingredients? (don't eat it). These questions probably do not encompass all the things you could look for, but it's a start.
I think training yourself to flip a package over and reading the ingredients is important. Honestly, most of the foods I buy do not have a package. They are single ingredients. Apples. Lettuce. Eggs. Beef, etc...the only real time I check is with dried fruit and nuts, which is my favorite most portable snack. I prefer fresh fruits and veggies for snacks, but if you are stuck on campus, some homemade trail mix is awesome. Unsalted nuts and unsweetened dried fruits.
I think the easiest way I have eased into the omega-3/-6 thing is, if I eat a food at some point in the day that is high in omega-6, I try to eat something else that is high in omega-3. An example: nuts are higher in o-6s, so I try to eat a piece of fatty fish high in o-3s at some point in the day. It seems easier to get the o-6s, so I try to counter it by sprinkling flax seeds on salads which are higher in o-3s. This is probably a pretty rudimentary way of doing it, but it's easy for me to do as I am beginning as well.