Watch the Bending Notes online guitar lesson by Annie Raines from Blues Harmonica Blueprint
The best way I’ve found to get clean, fluent bends (after lots of frustrated attempts), is to use a combination of phonetic sounds and a relaxed throat, but I’ve seen Piedmont Blues phenom Phil Wiggins teach bending to his beginning students with great success using the lip method. Tilting the comb of the harp down towards your bottom lip can help you get a bend right away. It’s important, though, to stay physically and mentally flexible about harp positioning. There are lots of perfect angles and perfect spots for producing sounds; don’t limit yourself to just one.
Bending can be very frustrating to learn so give yourself lots of breaks and keep trying. Try to keep your lips and cheeks relaxed and save your energy for other things. Remember that it’s easier to block air with a relaxed tongue than a tense one.
Here are a few phonetic sounds you can use to shrink the aperture and lower the pitch (more on the video breakdown):
Eagle (hold the "L" sound towards the back of your throat if you can. (While on the subject of birds, try "seagull")
Note: these techniques rely on guttural sounds and seem to come more easily to speakers of Germanic languages. Ich bin ein Bender!