I agree with everything here so far. I just wanted to toss my $.02 in for the sake of hearing my own head rattle...
From what I have been reading elsewhere on the Internet on this topic, I have found these statements regarding lyrical hooks and what they have in common:
Lyrical hooks often are found in song tiles, in choruses, as the climax or introductory statement of "what the song's about" phrases and so on.
Lyrical hooks tend to be short, easy to say, melodically interesting (use chord tone intervals, 3rds, 5ths, 7ths...) and repeatable (by the listener) as well as repeated by the singer(s).
Lyrical hooks commonly have an obvious rhyme scheme and meter.
Lyrical hooks leverage commonly heard phrases and sometimes simply twist them slightly to make them stick out.
For me, when I am trying to think if a particular phrase that might have "hooky qualities" I use the "Children's playground chant" rule of thumb to test it out. This rule of thumb is; if you can hear your phrase becoming the kind of thing you would hear kids chant repeatedly while jumping rope or playing those paddy-cake style clapping games, you probably have the makings of lyrical hook on your hands.
"Eenie Meenie Minee moe, catch a tiger by his toe, if he hollers let him go"
"I get knocked down, but I get up again, you ain't never gonna keep me down"
"Ikka bikka soda cracker, ikka bikka boo... ikka bikka soda cracker, out goes you"
"De do, do, do... De da, da, da... is all I want to say to you..."
So if you can easily hear the playground kids repeating your phrase, go with it.
Much of that playground philosophy carries over to melodic hooks as well.
"Nah-nee nah-nee nah nah"
"Rain, rain, go away, come again another day"
A certain symmetrical quality or balance also needs to be there. It seems that, in short, a hook - even as short as it is - needs to start and complete a shape.
"De do, do do, De da, da da..." = (up the first side of the hill)
"Is all I want to say to you..." = (down the other side)
Also - it seems that a good hook is one that you can mentally incorporate into a nice walk. So, ballads and speed-metal aside, a phrase that has a nice, up-beat pace that can be chanted as one takes a nice brisk walk on a warm summer eve seems to work well.
So - in your mind, if you can:
Hear kids chanting it
Hear kids singing it
Find it to be balanced
Can use it to set a mental cadence for a nice walk
...you are probably working with a good pop hook.
I think.