Go with a subtle approach. Many labels on jelly jars are quiet, allowing the jelly itself to be presented without much visual interruption. A lot of homemade jellies opt for the minimalist label, so if you're aiming for a makeshift look, the mantra "less is more" would be an effective idea.
Alter the shape of the label. Many labels are traditionally rectangular in shape, so stray from the norm to gather attention. If you are making a label for jelly jars to be sold in stores, you have three seconds to capture your customer's attention before they move on. Making an oddly shaped label can spur intrigue from a distance.
Think about the lid and other characteristics of the jar to utilize. Having a symbol on top of the lid will characterize the jelly jar before even getting to the label itself. The lid is a great spot to use for information when your label is too crowded.
Experiment with different sizes of labels. Many jelly jar labels are only on the front, leaving the rest of the jar translucent. Try different wrap-around labels to see which would work best for the specific jelly jar in question. Being the lone wolf in a pack of similar products can catch eyes much quicker than the others.