Theres a great tut video on the gome page of this site. Of course thats for a liberty spike mohawk not full head liberty spikes, so im assuming your talking about the mohawk
when I put my bfs mohawk up in liberty spikes I section his hair into 5 equal bits, then get a comb and pull his hair up taught and use loads of hairspray at the base and blow dry it, spray more and blow dry again. Then move onto another section and do the same until they're all mostly up. Then I twist and spray the tips and dry. It normally stays up for a few days.