i write elements that go for

1/2bar
1bar
2bar
4bar
3bar if i want evolution of a sound
8bar
and 16bars

I also make sure i have stab/fx/earcandy/melodies that meet each other and create a pattern within a pattern over the 16bars.

The most important thing you can do is ensure that you velocities alter over time especially with highly repetetive stuff.

A slight flange or unsyncd chorus can help a loop retain some feeling.