Def Leppard-Yeah!, 2006
1)Pick songs you truly like. I know that sounds simple, but I think many times bands pick songs or artists that they think fans want to hear rather than what they like. I think Def Leppard picked songs they enjoyed and artists they liked no matter what their fans may think.
2)Put your own sound into it. Again this sounds simple, but too often bands try to do a note for note cover and forget to put their own style into it. If you can't add something to it then you should not be recording it because there is no point to just repeating a song.
3)Have fun with it. This goes hand in hand with number one, but if you are not excited about it then that will come across. I have heard so many dry, lame cover songs that I cannot even make it all the way through because the bands sound they are just trudging through it. I am talking bands I normally like as well. Again if you can't get excited about the song then choose another song.
4)This is more a production issue, but there is no need to make a song too slick. Particularly if the original had a raw sound. Ozzy's cover album from last year did this and it was just horrible (although not the only thing horrible about that album).
I don't normally see the point in doing a cover album because I would rather hear a band work on originals. This album is not great, but it is good and it sounds like they had fun doing it. So hats off to Def Leppard for this.