What are some tricks for avoiding the tu/vous dilemma?

Ne pas adresser la parole à la personne concernée
Parler seulement de généralités en évitant de s’adresser directement à la personne
Parler toujours au pluriel

There are several strategies.

Change the whole focus of the sentence. For instance, you want to flatter the person by asking “did you cook this meal yourself?” (knowing that he/she did cook it indeed), you’d be tempted to ask avez-vous cuisiné ce plat vous-même? ; you’ll have to ask ce plat est délicieux, qui l’a cuisiné ? instead.
For “your”, instead of ton/votre, always use ce. You want to borrow something, you won’t ask it like “puis-je emprunter ton/votre …” but either “puis-je emprunter ce …”.
If talking to someone you know very well from an organisation, like a different company, but you’re not sure of the context (formal/informal?) just always say vous and pretend you talk about the organisation as a whole, which is always a plural, if you get any remark.
Sometimes, you just can’t. In this case, use vous repeatedly until the person makes clear that the tu is ok. 🙂
Some people have the dirty habit of using neither vous nor tu but will use a third-person instead. Typical from shop owners who want to sound a little fancy: Et il lui faudra quoi au monsieur? Do not do that.

Use this simple rule: use vous by default.

I often ask if I can use tu after a couple of sentences. The answer is always yes.

Use “tu” and say “My mother tongue is english, I don’t do such difference” and smile

Another trick as I discovered by answering another question : sometimes, you can use nous:

I’m not saying it’s always applicable, and it will sound weird in a lot of cases, but it’s worth knowing.

As already mentionned, the third person can also be used, but probably only butlers can pull that one off: