Ok, here the main game is:
- get a card with a sweet bonus
- meet the Minimum Spend
- get some bonus points
- downgrade it at the end of your first year
Who can do this? Anyone who can get approved for sweet credit cards. (if you can’t get approved, then get some less-prestigious credit cards with no fees, use them for a while, always pay them off, and eventually your credit rating will be better and you’ll get approved.
You might not want to do this if you’re buying a house soon - it’ll ding your credit just a bit. But that wears off.

1. Get a card with a sweet bonus.
You’re looking for, ideally, 30-50k points/miles, and annual fee waived for the first year. Some of these that I’ve done include:
Barclay AAdvantage Aviator Red
Barclaycard Arrival Plus
Capital One Visa Signature
Chase Sapphire Preferred
Chase IHG Rewards Club
Chase MileagePlus Explorer
Citi ThankYou Premier
Citi American Airlines AAdvantage Platinum Select

Maybe check r/churning to see what’s popular now. Sometimes there are particularly good deals (like the MileagePlus Explorer is usually 30k miles but sometimes 50k), so try to jump on those. The Chase Sapphire Reserved was even 100,000 miles when it first came out! 100k deals usually don’t last long, though. If I see a 100k I’ll jump on it; and usually a 50k is worth it too.
Note that, to me, hotel miles are worth about half of airline miles. So if you’re looking at a hotel card, try cutting those values in half.

Ideally this will be in an airline/hotel you want to use, or use often, or a convertible rewards program. For example, Tati and I had our wedding planned at an IHG hotel in Pittsburgh, so I used the IHG points I got from this thing to book us some free rooms. And I fly United a lot, so those miles will get used.
Convertible rewards programs are stuff like Chase Ultimate Rewards or Citi ThankYou. These are points that you can convert into specific airline/hotel miles, or sometimes use them for other things too.

2. Meet the Minimum Spend
All these deals will have some kind of minimum spend to get the big bonus, like “50,000 bonus miles after you spend $3000 in the first 3 months.” Just start using the card for everything. If you wouldn’t end up spending that much in 3 months, there are ways to spend a small fee to “buy” points - just look up “manufactured spend” on r/churning. For this reason, I usually don’t churn more than one card at a time - it can be hard to meet the MS on all of them.

3. Get the points
They’ll usually automatically post with little fanfare, and it’s not usually as soon as you meet the minimum spend, so you might have to check on it a little bit.

4. Downgrade at 1 year
The CC companies are trying to get you to start paying the annual fee (after they waive it for the first year). You just have to remember to “downgrade” your card - roughly, trade it in for a “lesser” card with no annual fee. Like, I traded an AAdvantage Platinum Select ($90ish fee) for an AAdvantage Bronze (no fee). Course, the AAdvantage Bronze has no big perks… but that’s ok, because at this point, you stick it in a drawer and don’t really use it for anything.

To do this, just call them, at the number on the card or wherever. Ask them to downgrade this account to a no-fee card. They are usually more than happy to help. They’ll often have a bunch of different ones - it doesn’t matter which one you pick, because you’re not going to use it anyway. You can usually do this a little after the 1 year mark; then they’ll refund your annual fee. Sometimes they’ll let you do it before 1 year.

An added benefit of this is you now have more credit available to you, which improves your credit score. If they won’t downgrade your card, you could always just close the account. But I think I’ve only had that happen once.

Total benefit: ~50k points, up to 3-4 times a year. 1 point is worth roughly $0.01, so we’re talking ~$500 each time.
Total cost: $0.
Total effort: well, nonzero. But it’s not terribly a lot of work.