Constraits are good. Fighting with and working against rules that you have set for yourself can be a great way to open up your mind and face challenges in a new way.
Limit what tools you have available. Use limited colours, use only one pen, only one pencil.
To start with you might like to try this for your idea generation stage of a project but after a while this can take over all of your work. It can be very difficult. It can be very freeing.
See full post here: iain welch2014-10-30.