Sluggish Mac

Hello Applie cousins.

Whilst I use iOS devices everyday, I have virtually no experience of Mac OS since OS 8. I occasionally use my wife's macbook, but it's just not *nix enough for me...

However, we have a problem, and as the nerd in our relationship, I've been tasked with fixing it. Said macbook (mid 2010 model, now 4GB RAM) has been pretty reliable, but it's recently slowed to a near halt. Opening simple apps takes >30 seconds, as does opening new tabs in Safari / Chrome.

I don't really know where to start, so what should I do first? Reinstall OS X? We're now on Mavericks, and have never reinstalled.