I use a small pair of plastic pliers to guide the connector to the socket. The keyboard/trackpad connector is the last connector you clip before closing the top case.
First enter the AC adapter port to the top case hole then align and connet the power switch connector in his socket with a plastic spudger then connect the speakers connector to the speaker socket with the spunger. Once this connector is in place and well connected enter about half to 3/4 inch of the speaker cable in the hole over the speaker socket, if you don't do that you'll have problem to close the top case. Last connector to connect is the keyboard/trackpad connector. Use a small flashlight and light the connector while you're ajusting the top case just over the connector. If you don't have the plastic pliers use the spunger to guide the connector over the socket pins and push it down carefully. If it is not well aligned you will fell a resistance so don't put too much force.
Also (I often made that mistake) before installing the top case on the ibook G4 800 to 1.2Ghz models double-check if the sleep magnet is there under the top case cause the sleep function will not work and you'll have to reopen the case.