Typically, the drummer will put a fill in the measure right before a new section. So try putting a fill in at the end of your verse going into the chorus, or going from the chorus to a bridge section. Don't forget to add a cymbal after the fill, on the downbeat of the following measure.
You can also use fills for pickup notes when the drums come into the beginning of the song, or when they’re coming back in from a break without drums. A drummer will almost always put in some kind of short fill before going back into the groove. Don’t forget to add a crash cymbal on the downbeat of the measure after the fill.
You can easily use just half of a fill instead of the full measure. In other words, if you want a shorter fill, like 2 beats instead of the full 4, you can simply set your program’s Snap Grid to half-note, then shorten the loop by two beats and place the fill on beat 3. You can either use the first two beats of the fill, or the last two. Then, just extend the loop that’s right before the fill by an extra two beats so it butts-up against the two beat fill you created.