Strings are very important, don't let anybody tell you otherwise. From ukulele to double bass, the kind of string you use is a huge factor in the sound that will come from your instrument. Finding the right gauge (thickness) is the first step in finding your perfect string match. Make sure your instrument is setup properly otherwise you may be dooming yourself from the get go. I always recommend starting with light gauge since that's right in the middle of the gauge spectrum. If you feel like you want a thicker, heavier feel then you can move up to mediums, heavy's, or some kind of hybrid set. If you want a looser, slinkier feel then you can go to a thinner set like custom or extra lights. As with the instruments, there are more string companies now than ever before so, once you've found your gauge, try a different brand of that gauge every time you restring your instrument. Some companies use different mixes of metals in their strings and some have different core tensions so take note of what you like and dislike about each brand and use that as a reference for your next choice.
Until you settle on the perfect brand and gauge, always keep the empty pack of whatever strings your currently using in your case/gigbag so you don't forget what your using. I can't tell you how many times people come in the shop and say "I love the strings on my guitar but I forget what I used. Can you tell me what these are?" Unfortunately most strings look the same so it's very hard to accurately answer this question so the best we can do is measure the thickness and get you something that's the same gauge.
As always, consult your friendly guitar store employee to get a good recommendation and to answer any string questions you might have.