Have you tried the 3rd ed. AISC manual? There's a procedure there describing both strength and stiffness requirements for beam bracing. You need to figure out what you want to assume for bracing and then figure out your strength and stiffness requirements. From there you can see if your details meet those or if they need to be altered.
For instance, if your joists beared on the beam on a bearing plate and were toe-nailed, that probably isn't good enough to brace the beam. If on the other hand your floor sheathing was fastened to the beam flange directly with powder-driven fasteners and the floor sheathing attached to shear walls, then you're probably braced pretty well.
As Dave said, it can be very intuitive and is part of the art of engineering as opposed to the science. Given some rational engineering analysis and jugdment you can usually figure it out and be pretty safe. Besides the AISC manual, you can also look in Salmon and Johnson's Steel Strucutures. They have a rational method for designing beam bracing also. Keep in mind it is out dated, but probably works. For my part I assume a larger unbraced length than the joist spacing, say midspan bracing for instance, and things work out fine, but that's what makes me and my boss comfortable. You may be ok with something different. I'd go with the text book, the AISC and some gut feeling and see what you come up with.
