I am just a beginner on mandolin, and I am still tuning to my boyfriend's guitar so we are playing in tune.  Maybe I need a better set of strings, if anyone has a preferred brand that they can recommend, please...  We just replaced mine a few weeks ago, and they already go out of tune faster than I expected. 

BTW, I had a really tough time remembering which string was which, esp. because I had learned most of the guitar strings and how to tune them - I could not keep the mandolin strings' order straight in my mind...  So, a friend helped me out by telling me to remember G-D-A-E; he pronounces it in a semi-Australian accent as if he is saying "G'day" (i.e. g'day mate!)  Anyway, all I have to do is say g'dae and I have my strings in order.