I found the following paper interesting.
http://www.archive.org/stream/exercisesinmelo01goetgoog
In a nut shell the first 30 or so pages:
Two close notes no more distant than a tone then a skip of at least a 3rd. What you land on then seems to be the important fact., i.e. if you land on the tonal center notes 1-3-5 feel free to move up scale or down scale as the 1-3-5 are tonal center notes and thus happy anywhere.
The 4, 6 and 7 notes however, are wanting to resolve to the tonic and have a set way they like to do this so........
If you land on a 7th go up scale and start the process over.
If you land on a 4 or 6 go down scale to start the process.
If you land on a 2 - the book was not clear (in the part I finished), but it's kinda left up to you.
Two short steps followed by a skip - then depending on what you land on governs what you do next.
http://www.archive.org/stream/exercisesinmelo01goetgoog
Check out chapter 3.
Course if you JUST do that over and over it too will sound the same, I think it's the distance of the skip that is important. Vary the distance, don't land on the same interval. Mix this in with what you are already doing should give you something new.
Have fun.