It’s not the most fun job to tackle, but here are some ideas to help you do it faster.
Whenever possible, get the joist hangers in place before you install your beam. Of course, this means you have to be very careful in positioning the hangers, so they’re not too high or too low.
To speed things up, make a simple jig from scrap lumber.
Start with a 30″ length of 2×6 as a top plate, and nail a 2×4 (or scrap end of joist) to the 2×6 to simulate the joist position. Measure down the 2×6 a precise joist spacing and nail another 2×4.
Now you simply fit two joist hangers to the jig, and rest the 2×6 along the top edge of your beam. Nail your two hangers in place and move on to the next. By placing one end of the jig in the hanger you’ve just installed, it’s easy to position the next one without measuring. (For this to work, all your joists must be the same width. Line them up beforehand and check for variances.)
Use those metal barbs on the joist hangers to help position the hanger, rather than trying to hold it in place as you nail. If you’re a little off, it’s easy to tap it into position.
Always remember to nail ALL holes of the joist hanger. And drive them at opposite angles to prevent the slightest chance of pulling out.