1. Keep practicing speaking frequently, ideally with native speakers. I bet your writing skills are so good because you've unknowingly perfected them over the years of reading and writing comments, posts, etc on the Internet. Therefore, the same goes with speaking, you gotta tough it out and give it time until yours can improve.
2. Try dubber ducking to yourself out loud new concepts/things (in English) you've learned, even better if you could find someone to listen to/explain to.
3. Have mock interviews, ideally with somebody who's in the industry so they could come up with interesting questions on the spot, which would force you to have to learn to come up with suitable answers.
4. (I don't see myself ever doing this but worth suggesting nevertheless) Start a podcast or vlog discussing technical topics (without scripts.)