Where do I start?
First, draw your workflow. If you plan your workflow well, the rest will be straightforward. I can't stress this enough - if you don't plan, you'll very likely find the whole experience very frustrating.
List the users or roles involved and identify what each one needs to do and at which stage. Try to separate the process into distinct steps involving approval and user input. You may find it useful to draw the process using a swim lane diagram. Pencil and paper is perfectly sufficient but you may like to use software like Visio or an online tool like gliffy.com or draw.io. Draw one column per person or role and then add the actions in the appropriate columns.
Create a form to use for your workflow. This form must contain all the fields used at every step of the process but don't worry if you need to add fields later.