Most advice about loyalty points is written for businesses. This one is for the person collecting.
How earning actually works
Programs come in two shapes and the difference decides how you should use them.
Stamp cards count visits. One stamp per qualifying purchase, a free item once the card is full. What you spend does not matter, so a stamp card rewards you for coming often rather than for spending a lot.
Points programs count money. Points per pound, a reward at a threshold. These reward larger baskets, which makes them better value if you occasionally spend a lot in one go.
If you know which type you are in, you know how to get the most out of it. On a stamp card, more separate visits beats fewer large ones. On a points card, it makes no difference.
The main ways people lose out
Not presenting the card. This is by far the most common. The moment to scan or hand over the card is when you are paying, not after. Once the transaction is closed, adding it becomes a favour rather than a process.
Carrying a paper card you will lose. If the business offers a digital version, take it. Paper cards go through wash cycles and get thrown out during tidies, and there is usually no way to recover the stamps.
Not asking when it was missed. If staff forget, say so immediately. Almost every business will add it there and then. Very few will do it three days later.
Letting points lapse. Most expiry is based on inactivity, six or twelve months without a purchase, rather than a fixed date. If you are close to a reward at somewhere you have stopped visiting, one small purchase usually resets the clock. Check the terms first.
Joining programs at places you rarely visit. A card you cannot realistically finish is not a reward, it is a mailing list signup. Be selective.
Programs worth joining
Ask three questions before you sign up.
Can I reach the reward at my normal rate? Work it out honestly. If you buy coffee there twice a month and the card needs ten stamps, that is five months. Reasonable. If the card needs twenty, it is not.
Is the reward something I actually want? A free coffee at a place you like is worth having. A voucher toward a product you would never buy is not.
What does it cost me to join? An email address is normal. A phone number is common. A full app download for a single shop is usually not worth it unless you are there weekly.
Getting more from a program you are already in
Ask about bonus days. Many businesses run double stamps on their quietest day and mention it nowhere. If you are flexible about when you visit, this halves the time to your reward.
Check whether a bigger order earns more. On a stamp card, buying four coffees at once often earns one stamp rather than four. If you are doing a coffee run, ask. Some businesses give one per item, some one per transaction.
Use the welcome offer. Many programs give a stamp or a small reward at signup. Join before you order rather than after, so the first purchase counts.
Add the card to your phone's wallet. If the business uses Apple Wallet or Google Wallet, the card can appear on your lock screen when you are near the shop. This is the single most effective way to stop forgetting to scan.
Say when it is your birthday. If the program asks, answer. Birthday rewards are common and cost the business almost nothing, which is why they are generous.
When a reward is nearly due
Two practical points.
Rewards are usually claimed at the counter and cannot be applied retrospectively, so mention it before you order rather than after you have paid.
If a card is close to expiring and you cannot get in, ask. Small businesses in particular will almost always honour it, because the alternative is losing a customer over a rule they wrote themselves.
If you run a business rather than collect from one
The mirror image of everything above is worth reading. Most lost rewards are lost to friction that the business created and could remove: no digital option, no way to fix a missed stamp, an expiry nobody was told about.
How to create a loyalty program covers designing one that people can actually finish.