Mentor must be licensed architect.

also hours that are easy to finish in school:

Site visit with mentor will get you some construction administration hours, if your campus has a campus architect make them your mentor and visit construction sites with them.            ( these are some of the hardest hours to get)

also volunteer to be on design juries for the undergrad studios.

Getting a mentor is as easy as asking someone to be your mentor. My mentor is a former professor of mine that I developed a good friendship with. I don't know if that is unusual, but for me, it made perfect sense. He knows what goes on in an architecture office and if I ever have a question about how a typical firm might practice, I would trust his response. I have never had him sign off on any hours because I haven't pursued those options for hours.

People will tell you that ideally a mentor should be someone who is not at the same office you work at. This allows them to give you good advice without worrying about internal office policies or politics, etc. NCARB says that they must be a registered architect. Keep in mind that there are very few opportunities for hours where your mentor will sign off on them compared to the hours your supervisor will need to approve.

So, you'll also need a supervisor to sign off on your hours. This is someone that is a registered architect and directly supervises your work (i.e. your employer). Generally, this is someone that you don't really get to pick (they are just your supervisor), unless your employer lets you pick who you work under. There are opportunities in experience setting O that don't require the supervisor to be a registered architect (like if you are working for a contractor or engineer). 

Good luck. Also, keep in mind that next week this is getting overhauled, so before you get too caught up in it, you might wait for the new AXP guidelines to be released to verify requirements for mentors, supervisors, etc. I wouldn't anticipate any changes from the current, but you never know. The link above does note that some experience options will be gone in the new AXP.

Wow thanks for the heads up. I was considering seeking post professional M.Arch program particularly for the Advanced Hours just to find that, starting June 29, they will no longer count. 

Some AIA chapters will help match interns with mentors.  

What state are you in? There are a few that have state-specific rules that disallow experience hours earned before graduation.  A few states also have extra rules about supervisors' experience - for example requiring that they have been licensed in that particular state for a minimum of 3 consecutive years before they can supervise interns there.  Check into those things, because otherwise you can find that you've satisfied all of NCARB's rules for IDP and yet still need to get additional experience to be licensed in your state of choice.