From Victor Navone's Blog, a really good article about the phrasing in your animation. Mixing up the tempo so not everything is hitting on the same beat. This really adds to the appeal/entertainment of your animation.___________________________________________________________
Something I heard back when I was first learning animation that still really helps me to this day: always try to get three speeds in your shot. Put in slow moves, medium moves, and fast moves. This will help give your shot texture, interest, and emphasis. If you can have different parts of the body moving at different speeds, even better! Take a look at this clip from 101 Dalmatians. This animation is beautiful in many ways, all of which I wont go into here, but pay particular attention to the timing of the actions. Pongo is sleepy, so naturally there are lots of slow movements. But there are also faster moves for emphasis, such as the ear scratch, the collapse at the end where he lets gravity take over, or the high frequency shaking during the stretch. Not only are there three different speeds of animation, but some of these speeds are happening simultaneously. Another example would be to have a character shaking his head as he raises his arms up slowly in anticipation of a gesture. The more variation you can add to your timing, the better. I see a lot of student work where the characters are always moving in a "snappy" fashion. This is fun to watch for a while, but soon the timing becomes boring because there is no contrast. So don't forget to shift gears!