As an engineer/YC founder turned B2B go-to-market/sales leader, I can attest that it's hard to learn sales without jumping in and doing it. That said, a few things helped me along the way:
1) I found a mentor that I could relate too, one that did exactly what I was trying to do (an aside, I ended up joining a company called Boomtrain and learned how to sell while helping him build product -- this hybrid role evolved into starting and running their Solutions Engineering team.)
2) Be OK with being uncomfortable; a lot of sales is about putting yourself out there -- you're going to get rejection, but you start to learn how to place your bets and work in the opportunities that have the highest likelihood of closing (and therefore can be well-forecasted.) This is where a sales methodology helps. Calvin (the CTO of Segment) wrote this amazing blog post about about what we use on our Sales team: https://segment.com/blog/how-to-sell-a-b2b-product/
3) Spend the time building a defined process, whether it's generating top of the funnel/leads, moving deals through sales stages, and even a deal-desk process for inking MSAs/contracts. Invest in a CRM (I suggest Salesforce) to log everything and provide visibility on your business, while helping to manage the pipeline.
Happy to share more details about my journey so far.