Marketing/PR background looking to transition into Proposal Writing

I currently work as a program coordinator for a college and I am looking to make a career transition into proposal writing on down the road. I have a background in Marketing and Public Relations and utilize a lot of those skills in my current position. I have also written marketing plans and have assisted my boss with writing business proposals in the past. I am also collaborating with the grant writing department to learn grant writing as well. I am trying to figure what steps I need to take in order to get into proposal writing as a career on down the road, including what certifications I may need to pursue as well as what steps I can take in my current position. Any advice would be greatly appreciated!