There are many ways to determine which efforts are producing results and which ones aren't. For example, you can study your website's analytics through your web host or by using Google Analytics. Most social media sites provide analytics as well, or you can use tools such as Hootsuite to get social media analytics. Your email service should also provide you with information on the open rates and engagement rates for your emails.
There are a lot of items that can be purchased very inexpensively at garage sales or thrift stores and sold for higher prices elsewhere. A few years ago I discovered that I could purchase good hardcover books at my local thrift shop for $1 or less. I realized that some of them could be sold on Amazon.com for $15-$20, which turns out to be a pretty decent profit.