You will find tons of good info here. Does your plane have to be of your own design, or would a kit or printable plans be appropriate? If it has to be, or if you want it to be your own design, there are some factors to look at and think about, that would otherwise be solved and the thinking done for you were you to use a kit or plan. What type of plane is it, where is the prop located? The most basic issues that usually mess up home designs are usually related to motor thrust angle or center of gravity. If it isn't one of these two things, some other common issues are wing loading(your plane is just straight up too heavy), electronics or linkage issues, or pilot error, such as over-controlling(especially bad on a touchy or rough design, and even worse if your transmitter does not have expo.)
So the main questions are, what type of plane is it?(pics help). Is it your own design from scratch, or your own design based on a historical plane or proposed model or current RC plane? Is it a kit, or maybe a plan you found somewhere or purchased? What materials are you using to build it? Dollar store foam board or other? What is your electronics setup, and what sort of transmitter are you using?