There is some parlay advice in this famous book
http://www.stavochka.com/files/Sharp_Sports_Betting.pdf
In general I find it helpful to keep your parlays of reasonable size not taking too many selections. It can be helpful to determine how much you would like to win and build your parlay with this goal in mind.
You can also give yourself some room for error by eliminating some spread lines of favorites in games you are not certain about and replacing those selections with the money line in the parlay.
It is not a good idea to include many underdog money lines in parlays. If you like the underdog to win outright, make a straight bet on that game.
Teasers can increase your chance of winning. Think of them as mini parlays. There is a section in the book on constructing better teasers as well.
At times I will build a parlay and build a teaser with the same selections. It gives you are margin for error and you can still win money if your teaser hits when your parlay misses by a few points.
