If your garden is not yet public, invest in a feeding table and put at least some green vegetables on it for wildlife; but (preferably) mixed vegetables, to attract your busy friends more often and speed the acquisition of those important diamonds. Visit your garden or someone else's and water at least one plant every time you collect your "3-hourly" gold, to try to spot another "crittur". Most of your visitors will be mice or mallards, but once your herb has fragrant leaves you may see a Brown Bunny or hare (each worth two diamonds) at times.
Remember your "twice daily" free Mini Mushroom Game tokens: you don't get more until 12 hours after you collected the last batch; maybe you should write each actual collection time in your diary so as to get back as soon as the next batch is there. You don't have to play immediately but can save your collected tokens for months at a time. When you do play, you have a chance of winning little prizes, which may include gold or diamonds.
Once your garden is public, there is less urgency, because you can attract other fairies.
When you visit any other garden, leave a friendly note and tell its owners (and their next visitors) what you have to attract them to your garden.