How can I prevent wasps from nesting in my eaves?
Wasps do not like strong mint fragrance. You could apply mint essence/oils to the problem areas, though I'm not sure if you'll get a whole season of protection from a single application, so you may need to reapply every few weeks. For a more permanent solution you can plant mint, citronella, or other insect repelling plants. Just be aware that practically all mint varieties spread aggressively and are nearly impossible to completely eradicate if you change your mind later. Planting in pots may be preferable.

Using decoy nests appears to come with mixed reports of success. These are a fairly inexpensive way to address the problem, that you can set and forget. Judging from the review sentiment, it appears to be important that you get your decoys up before the wasps show up in spring. If you're too late they'll ignore the decoy or worse, they'll use it as a foundation for their own nest.