The answer depends on what you sell. If you sell an enterprise product to big corps then the patio11's guide [1] would be a good starting point.

Otherwise, selling is simple - just solve the customer's problem as if it was your problem.

What's really hard is marketing. And you will need marketing because marketing generates leads and without a stream of leads you can't do sales.

[1] https://training.kalzumeus.com/newsletters/archive/enterpris...