I would imagine before you start working as a Linesman extensive in housetraining will be required, climbing sklls, fitness levels etc, you could bone up on the sklls required on the internet I shouldn't wonder.
What voltages will you be working on, HV or LV these are topics you could ask during and after your interview, there is bound to be some information floating about, you could get hold of. I suppose the best help would be as well informed about the type of work you will be expected to carry out, research the company interviewing you, ask questions regarding H&S, what training will be required, and how long will the traing be, will it be intensive training, or on the job training, if you have any electrical experience, ask if any of it will be relevant, the list is endless realy, just be as well informed as you can, and good luck.