For this small article a few pointers about what you can do to make your coversongs sound better.
Most beginners will start out with playing songs they know, they may look for some tabs or get the chords for the song they would like to play.
Once you play through the chords you may feel there is something missing: The introduction to the song contains some single notes, is this little melody in your given tab, or is it left out to simplify the song? The chords are all wrong, or they seem to work but they do not sound anything like the ones being played in the song. Look again for another set of chords. Maybe the chords you have found are simplified, they may be in a different key from the original song. The original song my contain barre-chords, at the moment this may be too much for you yet, so the chords you may have found may not be playable for you at the moment. Look for a simpler version of the song which still reminds you about the sound of the original song.
Whenever you want to play a song by someone else, first listen to the original song, make sure you know how to strum the chords. In case you want to sing the melody as well, check if you can sing along with the chords, is the melody not too high? Maybe you need to transpose the song to another key for you to make it possible to sing along with the chords. Trying to sing a melody which is too high for your voice is not going to work, you will strain your voice by trying to sing in this manner. See if you can bring down the key and sing the same song again but now with the newly, transposed set of chords. The song will probably sound a lot better in this new key.
Playing songs is all a matter of doing it. You will find that the songs you started out with will sound so much better after you have played them for a few months. Once you have a repertoire of about 20 songs you will find that some songs will sound more natural for you to play and sing. Look at what kind of style these songs are and carry on playing more songs of this kind. It will make you understand the style better and you will also develop more as a musician, singer and guitarplayer. Once you feel you understand the style you have been playing for while it may be time to move on to another style to broaden your horizon and to keep up your interests in the guitar.