While you likely have other criteria that's more important, the fastest way would be to give each visitor a cash payment they would consider sufficient. The news would spread quickly with a high enough payment, and your site could easily see millions of visitors in a very short time.

My assumptions of what you mean by a "professional website" make it seem like the above visitors would not be your preferred demographic, who would probably be repelled by this 'fastest' approach.

I gave up marketing ages ago, but would suggest you study sites with the success you'd like to have. See how they did it, whether those techniques would still work, work for you, and all that. A/B testing is just one of the many aspects of marketing you need to become familiar with.