One approach I have seen that appears to work well is to make sure that your game has game play that happens outside of the initiative roll situations (either combat or skill challenges). This can be still in the middle of an adventure but since many rituals take both component costs and time to use if the game never slows down to a timeframe that accommodates using rituals players will likely gloss over and discount the value of them.
But when you give the players situations that aren't combat or the fast pace of skill challenges but do offer situations where rituals can resolve problems suddenly they become more valued resources.
If your players need further hints and guidance you could also introduce an NPC or two who use rituals to benefit (or hinder) the players - sometimes it takes an example to get people thinking of the options.
A factor to also keep in mind, however, is that non-ritual casters should have something to do to further the progress of the game while the ritual casters are spending game time resolving rituals (and/or researching them, gathering components etc).