Playlist is messed up

[mrthemesong]

When my songs are playing, it wil go from song number 1 to song number 18 then song number 3 then song number 7 but it is totally ramdon, there isn't a pattern. I beleive it is set to play random songs in my playlist. How do I change it so that song 2 will play after song 1 and Song 13 will play after song 12 and so forth.