If you want a sure-fire way to finish with a successful layout there is ONE thing you can do to ensure that.
That means pick ONE color from ONE picture and repeat it throughout your layout!
In this pocket page layout, I decided to repeat the color red which I got from the bleacher chairs behind Tyler.
We love ephemera but adding elements that have red already in them will always draw everything together.
I introduced another color, in this case is black, It's in small doses that I've included an accent color. That way it doesn't compete with the primary color.
Doing a monochroatic layout may make your finished product "flat". Add texture by height to add some shadowing!
Lastly, if you have more than one picture, it's helpful to make sure all the other pictures you've included are neutral in color. Again, no competition!
Good luck on your next 100% sure thing layout!