Give and Take
Canonical wishes are so often about gaining something, and there are problems in this world that could be solved by gaining a thing, abstract or material. But those classical stories go wrong in one way or another, and the root of all the turmoil is usually the object of the wish itself. This is why it is important to wish responsibly.
Any good wish, meaning any wish used wisely, should solve a problem. And most modern people would probably be tempted to wish for money, because in general, if you throw enough money at your problems, they go away. If this genie is into vague wishes, then this vague reasoning might be enough to get you money. But classical genies are notorious for being calculating two-faced creatures. They'll give you what you want, but it'll cost you big time if they can find a loophole in your wish. So if you don't want your life to go to heck in a hand basket, you better sit down with a lawyer or two, and draft up a seriously well thought out and well worded wish. Take your time. That genie's not going anywhere.
First and foremost, consider the wish for money.
When it comes to money wishes, people tend to wish for a set amount of money, like a trillion dollars. Don't do it, that money will run out eventually, and maybe sooner rather than later depending on how poorly worded your wish was.
Here's an example for you. You need to buy a pizza. But, there's a problem: you don't have enough money. You spent all trillion dollars or whatever. The problem would be solved if you did have the money. So, a good wish would be to always have enough money when you need it. There. Problem solved for all time.
But what if you've been stranded on a desert island? You need to eat, but in this hypothetical, you are on a literal desert island. There's nothing to eat, and nothing to drink. There's definitely not a convienent store from which to buy assorted necessities. In this case, the wish you just made to always have enough money is completely useless. Which is a problem.
So money's a good wish if you're planning on never getting stranded in the middle of nowhere. But since being stranded is not usually a voluntary choice, and considering that the genie will probably try to ruin your life in a variety of different ways, money is no longer the best possible wish you could make.
What, then, is the best possible wish?
Solve the problem of hunger by always having enough to eat and drink?
But what if you're drowning? Hunger's not an issue then, not having enough air is.
Classical wishes are most often phrased as gaining something. But, the need to gain might also be considered the problem of lacking. This, then, is one problem that might then be solved by wishing to always have what you need.