It's not necessarily time to change your strings, unless you have either played them so hard you can see shiny dings on the back where they have rubbed the frets or you just love that new string sound. It will make a huge difference though. The strings are you direct interface to the instrument - how you play them and how they vibrate is the heart of how you sound.
Have you any idea what was on there already? If it was a new bass, someone might know what they ship with; if a second-hand instrument, perhaps you have some old string packets floating around in the case.
And I'd guess the other questions to ask are how you want it to sound and what you don't like about it at present.
I'm no string expert when it comes to basses, but might have picked up a little info here and there.
They do break down and rust (a bit) just hanging on your ax, so if it's been a year, my vote is plunk down $25 for new ones. If you've never changed them since you owned the bass, it's definitely time now. Check out this site here for string reviews, description of the different types, and places to buy them.
Otherwise, I agree with Wulf and Toni. String choices can be overwhelming. If you want a place to start you can't really go wrong with a set of stock Fenders. If you want to go off the reservation, try a set of RotoSound 66s (love them on my Warwick) or Daddario XLs.
Another way to do this is hit Guitar Center or someplace where you can hear/feel the difference between round and flat wounds, steel vs nickel, etc. Hmmmmmm....I might do that this weekend.
Stainless Steel =Brightest, Piano sounding when new, lots of overtones , Finger noise, pick click,
Nickel = middle of the road , good all around string for playing any style
Half round = a round wound that has been grounded to be semi flat, darker sound.
flat wound = mellow ,warm. also thump, last for years,very good for retro sound ( my favorites)
nylon tape wound = very mellow , used a lot on acoustic bass and frettles , EQed right can come close to upright tone.