This! Especially if the job involves research of any kind. Try and find stuff you can't get off their wiki page too, because you can be sure they'll know what your likely sources are for the info you bring with you.
With regards to umms and eeerrrs, there's a handy trick worth remembering and that's think while you drink. Most interviewers will offer you a glass of water so it's simple enough to compose yourself mentally for your answer while you take a sip or two.
When you do answer, use evidence. They want to know about the times you used the skills you're being asked about, not vague assurances that you have those skills. You might be right, but it's like you saying 'mate, trust me!' with a cheeky wink if you can't back up what you say.
Finally, assume your competition are lying shits, so lie too.