How to develop your idea
Finding something in cells that might be valuable for the fundamental biological problem you work on.
Develop your cell-based assay in your home lab using dsRNAs you make yourself that target appropriate positive and negative controls (see the website: E-RNAi for help in designing dsRNAs).
At this point you need to define the biology you wish to examine, how you will measure/visualise this and check that your positive controls work and produce readouts clearly different from negative controls.
Given the range of possible biology being investigated we can’t really help you very much at this stage. However, a good rule of thumb is that screens should be as complicated as necessary and as simple as possible.