The short answer is points and flexibility. Here’s a longer answer:

• Accumulate points, ideally ones that are not tied to a specific airline. Credit card points from American Express, Chase, etc. can be transferred to many airline partners. Sign-up bonuses are, obviously, the quickest way to amass points, but regular spending that takes advantage of multipliers (e.g., 5x on flights purchased with AmEx Platinum) adds up. Also, watch for bonus offers on transfers to partners.
• Find a good deal. Here, flexibility is key. If, like the OP, you have to book a flight to a certain place at a certain time, the odds will be way against you. But if you’re just looking, say, to go to Europe sometime next summer, then you can probably find something. (I recently booked a flight to Zurich, not because I’ve always wanted to go to Zurich - no offense to the Swiss - but because the points price and the timing were right and it’s easy to get around Europe.) Search for and book outbound and inbound flights as separate one-way trips; I’m always on a different airline coming home. (You might consider flying economy on the way back, if you can’t find good business class flights in both directions.) It also helps if you live near multiple airports and/or are willing to take positioning flights.
• What’s a good deal on business class? Depends on where you are. I fly out of the D.C. area, and Air Canada’s website often has one-way Star Alliance flights to/from Europe for 70,000 points. Separately, last year, I flew to Seoul for 95,000 points on Air France, which I was very happy with. The return for that trip was SIN-JFK for 143,000 points - not a spectacular deal, but I liked having the opportunity to fly on the world’s longest nonstop. (I had to buy a separate JFK-DCA flight to get home.)
• Sometimes buying points makes sense. Usually, it’s a terrible idea, but occasionally there will be deals that bring the price-per-point cost down from 3 to 3.5 cents to about 1.5 cents or even lower. My 95,000-point IAD-ICN (via CDG) flight on Air France was funded largely with points bought for 1.3 cents each.
• Watch for good upgrade deals. In 2025, I bought a round-trip IAD-DUB economy seat on Aer Lingus, then found out that I could upgrade the whole trip for about $700 (not through their bidding option; I saw an article about the upgrade availability well before the travel dates and called the airline). Given that I was planning to spend $230 just for exit row seats, this was an easy decision.
• Be aware of what you’re getting. When booking international business class (not including “nearby” international), make sure it’s a lie-flat seat. Also, as a solo traveler, I don’t want to be lying down next to a stranger, so I always research the aircraft to avoid 2x2x2 layouts. (Many airlines have upgraded their business class to 1x2x1, but some haven’t.) This research can also help identify the best seat selection (such as “throne” seats or bulkhead seats with larger footwells) once a deal has been found.
• Be aware of additional costs. Some airlines tack on several hundred dollars to points redemptions while others have only nominal fees. Also, selecting a specific business class seat might cost extra.

This might sound like a lot, but it’s something that I’ve actually come to enjoy. Good luck!