Expanses or fields of color that resonate, that have depth, that reveal more the more you look, that shimmer in space, that's what you're after. Not blocks of flat, solid, opaque, dull color with sharp edges. Glazing is the secret, building up layers of color.
The 'secret' to successful glazing is to have the patience to allow layers to dry and transparent colors. If you're not sure what you're using, check the tube label or do a test. If you're painting with oils and get impatient waiting for a glaze to dry, work on more than one painting at a time swapping between canvases.
When you've finished, consider whether you're going to indicate on the back what you intend to be the top of the painting (see Abstract Art: Which Way is Up?) You could do this with an arrow, by writing the name of the painting, or your name. If you don't say which way it must go, you then mustn't get upset if someone hangs it upside down.