Ask them tons and tons of questions about their old job history and stuff.

 Write a list of questions you want to ask before the interview so you have some basis and watch the body language - it says a lot.

 Hi, first you be friendly with the guy or girl. Always the first question will be the PIR. (personal introduction round)
1. Tell me some thing about yourself.
2. Why did you leave the previous job?
3. How did you know about this or our company/
4. Speak on a topic for 1 minute (give one topic or let them choose one)
5. What are your strengths?
6. What are your weakness?
These are the general questions asked to see how communicative they are, you can check out their attitude, and if you are looking for the voice and accent the the one minute jam will show their thought flow and voice and accent. Always look whether the candidate is moving his hand, head, leg or fingers, even eyebrows this means he is not maintaining his body language (candidates who are giving this answers with a smile are preferred, some candidates give good answers but with serious expression mean they are not friendly in nature or caring attitude with them.