Going from flute to oboe is... interesting.
You start out on the instrument with the least resistance in the band and move to one of the most resistant ones (airwise). When I switched I found that I would run out of good air (oxygenated air) before I ran out of breath (any air in general) so I'd have to breathe out before I could take a new breath to avoid passing out.
Your best bet for help is finding an oboe teacher, but I can pass along some tips I've learned. (By the way, these will mostly have to do with mistakes I made as a beginner because I didn't have a teacher.)
1. Don't take in too much reed. Only the tip should be in your mouth, and if your lips are anywhere near the string you have WAY too much reed in your mouth.
2. Try to avoid biting the reed to control it. A clinician told me to think of your embouchure or your lips as a drawstring bag or of saying "o" and try to bring the corners of your mouth in. Biting, saying "e," and stretching the corners out, weaken the reed and are all bad, although biting is hard to avoid if you have an old or bad reed.
3. Get a film canister or something to put water in to wet your reeds with. Depending on the reed, you may or may not need to leave the reed in there soaking, a quick dip may do the job. In general though, the older the reed, the more it needs to soak. Wetting the reed in your mouth works in a pinch, but saliva breaks down reeds faster than water does. Oh yeah, change your water daily, for your sake.
4. Try to order reeds from an oboist who makes them by hand. Commercial reeds like Jones can be ok at first, but it's always a gamble on whether you'll get a good or even playable reed or not. I get my best reeds from Meg Cassell at
http://www.goodtoneguild.com although you should look around and test out other reedmakers to see who suits you.
5. NEVER use a plastic reed. When I started playing, my band director gave me a plastic reed. I couldn't play in all the registers, had no dynamics, and when I got home to show my parents, they asked me if the oboe was supposed to sound like a dying cat (for the record, it's not). To my knowledge, there are no plastic reeds available for oboe that aren't crappy. Even storebought, commercial reeds are a better choice.
6. Try to only use 'forked F' as an alternate fingering. If you learn the regular F it will sound better, and if your oboe has a 'left F' key, you should barely need 'forked F' at all. (Left 'F' is usually used to transition between F and Eb, D, Db, low C, low B, & low Bb. 'Forked F' will also do this, but if your oboe has a 'left F' key you should really learn to use it instead.)
This website
http://www.wfg.woodwind.org/oboe/ has a fingering chart so you can see what I mean. Where it says "Basic Fingering Chart for Oboe," click either "First Octave" or "Second Octave" (it doesn't matter) and look for the F fingering. The first listing is the one you should learn. The second is left 'F' which you should learn if your oboe has the 'left F' key, and the third and fourth are 'forked F.' This site is also good for checking out alternate and trill fingerings.
7. Get an instructor if at all possible. They can give you all the fine details on how to play correctly, and since they can actually watch and hear you play, they can correct any mistakes you make far more accurately than anyone on the internet, help you adjust your reeds (maybe even make reeds for you), and answer any questions you have.
There you go, that's a good start for a beginner, but really seriously consider getting an oboe teacher. There are so many things you can only learn by having someone there who can play for you and listen to you play and test your oboe and reeds, etc. I wish I had had one when I started out. Heck, I wish I had one now. I always learn more when I have one-on-one time with a professional musician than when I try to hack away at things by myself, and I think that's true for most people.
Good Luck and Practice Lots
