One of the main things to remember when programming MIDI is that every instrument has its own playing sensibilities and, consequently, inherent limitations. A common example is that a drummer only has two arms and two legs, and there's no way he's going to be able to play his hi-hat continuously throughout a huge fill.So if you are using for example one drum loop for rhythm and other for fill be sure that they don't overlap each other.On bars where goes fill just delete that portion of rhythm.Or if you step record drum part via midi keyboard be sure that you hitting just samples that would be possible for real drummer to reproduce(on real drums ).That way your drum tracks will sound more natural and it will be harder to distinguish if it is loop,midi or live played instrument.