Easiest notes to find

Cultivation Note - Till until you get it (Use your hoe.)
Sun Note - Work 10 hours on a sunny day non-stop
Cloud Note - Work 10 hours on a cloudy day non-stop
Snow Note - Work 10 hours on a snowy day non-stop
Rain Note - Work 10 hours on a rainy day non-stop
Island Note - Go to the island (First you must befriend the dolphin.)
Mole-Whacking Note - Whack a mole 10 times (You can only use your hammer!)
Rock Climbing Note - Climb the moutain (I waited until I was able to get the blue feather to get this one.)

There are a ton more that are really easy to get; especially when you befriend people. (I've become friends with Woody, Kurt, Joe, Tim, Katie, Eve, and a few more people.)