here are the basics: bonds have a TAG (trailing average gross), which is the average of their last 5 delisted movies (4 if they only have 4 delisted, 3 for three or less). once a movie delists with a star attached, the TAG adjusts, then the next day, the starbond price adjusts, just like a new release movie adjusts.
starbond prices and TAGs can differ quite a bit because the starbond price is set by the market, especially the farther out an adjust is for a bond. i usually find the best bond deals attached to movies that are probably 6 months from delist.
start looking through your portfolio of movies and check out the bonds. the high priced movies are a good place to start.
afj has given you the formula on the movies board. also, start watching the bonds that adjust, as sometimes they have another movie coming up that can earn big returns quickly. you just have to start somewhere and pay attention. here is a trick to quickly figure out a change in TAG: get the price of the next delisting movie (the current release or soon to be released), count five movies down from there (the last one included in the current TAG) and divide the difference by 5. add or subtract this from the TAG. this gives you what the new TAG will be when the current movie delists. compare it to the current starbond price. if there is a big difference, buy or short it. if it is basically the same, move on.
one final note. if a bond appears to be way over or under priced, look out for limited release movies that haven't delisted and therefore wouldn't be counted in the TAG. that throws off new bond players all the time.