Copy/paste all your loops and extend it to 4 minutes. Then try to mute something and listen to it how it sounds. Just try to imagine this loop in the intro. If it is ok, then start your track with that loop.
But it's a simple technique. If you want something interesting then you should create patterns (loops) for each section by itself. So, for example, create some pads in the intro but only in the intro. This loop should not play anywhere in the track but only in the intro. Try to change your chord progression in the middle of the track, it will sound interesting too.
Sometimes you can hear interesting things in some tracks, for example when your track is fading out and already near the end then you can hear that something new (synths, or leads, or melody) is starting to play. And you never heard this loop (or melody) before in this track. It surprises me all the time when I hear that technique but I am too lazy for doing something like that in the outro.