The most basic mixed progression is the staggered one.
You start with a limited negative progression line.
Shall you reach this limited negative progression's end, you start another one, with the base unit risen.
Example for even chances:
Stage one: 1, 2, 3.
Stage two: 2, 4, 6
Stage three: 3, 6, 9
Stage four: 4, 8, 12
And so on.
It is usually used with very limited progression lines and some like to throw in a parlay, a la "Risque (http://betselection.cc/mixed/the-risque-parlay/)".