Make sure the surfaces of the caliper where the pads sit are clean and free from rust/debris. Lube up the slider pins in the caliper. Make sure the brake fluid is clean and fresh. Make sure the pads - not the friction material - are coated witha thin layer of copper slip. Always best to do this yourself I think as most mechanics will just whip the old pads off and put the news ones off without inspecting, checking, cleaning, etc. Best to try and DIY it with someone overlooking what you do IMHO. Or read up on the info in the DIY section. That's how I learnt.