Firstly, just be warned you are swimming up stream! There are many more people out there with ideas but no development skills/financing than there are developers/financiers who are short of ideas. In essence you are saying "I want someone to build and support/finance this app, but I want x% because I came up with the idea but I can't contribute beyond that". Not necessarily appealing, and there is plenty of competition.
Warning done, the first thing you are going to want to do is to protect yourself. In order to pitch the idea to potential developers or funders, you are going to have to tell them the idea - at which point you are at risk of them running off and doing it without you. Before you get down to detail, make sure you get them to sign a Non-Disclosure Agreement (an "NDA") - it is a legal document that gives you some (but not complete) protection against this - Google "example NDA" and you will find plenty to crib from. Obviously you need to speak to a lawyer if you want to get it as tight as possible.
After that, just make sure you major on telling them what they are going to get out of this project, and that you have thoroughly researched the space so that your numbers have credence. For example, you might be able to tell them that there is no other app like yours out there so limited competition, but you would appeal to exactly the same customer group as apps A and B, both of whom have been in the top 10 apps for 37 of the last 50 weeks - suggesting revenue of x. etc etc.
Also be sure that you have thought the idea through thoroughly - if that is what you are bringing to the party then you had better be bringing it all, or the plan will fall apart. A sellable idea (I'll use Instagram) is not "My idea is an app that takes photos, but is different to the standard camera app" - your partners are going to have to do the hard work here, and will quickly find other opportunities. Better is "My idea is an app that takes photos but then allows you add filters like on old cameras so that they are unique and fun. The focus will then be on sharing them both within a community local to the app, but also on social networks such as Facebook and Twitter - where the photos will carry the branding of the App. It should be free of charge, but we will later make money once critical mass is achieved by y".
Hope this helps!