Not knowing Japanese will be a slight handicap, but there's plenty you'll be able to do without needing to say a word. You'd be shocked at just how many things you can buy by putting coins in a machine - lots of cheap restaurants use a vending machine system rather than having staff handle your money, similarly with a lot of tourist attractions that require tickets, and even in the middle of nowhere I've never had to interact with a human being to buy a train ticket. That said, I would recommend learning all the katakana (the Japanese letters used to transcribe foreign, usually English, words). You should be able to commit them to memory in a couple of hours, especially with the help of something like Slime Forest Adventure (http://lrnj.com/), and they'll come in very useful. Even without any Japanese vocabulary, knowing katakana will let you read a good few menu items at non-english-friendly restaurants and any number of useful signs. It's equally useful to familiarise yourself with the most basic Kanji, so you'll never find yourself standing outside a public toilet looking confused because you can't tell which door is which.
If you don't have a local person on hand to help you out, you're going to want a good guide book. I've been using Lonely Planet's Japan guide, and it's served me very well indeed. They do a more specialised Tokyo guide as well, which I imagine would be even better if you're not venturing far beyond the city.
If you're going in July, be prepared for it to be very hot. Like, regularly topping 37C. Maybe you're from Arizona or something and this isn't a problem, but if you're a northern european like me you might find it pretty draining.
Clothes shopping: buy clothes in Tokyo. Seriously. If you want cool clothes that none of your friends have ever seen before, Japanese labels can't be beat. Running from the northern end of Shibuya up into Harajuku is a rich seam of fashion gold, where anybody with (nearly) any budget will be able to find something awesome. I'm a big fan of Beams, Beams T, Graniph and Mono Comme Ca, so if you're male I recommend going out of your way for them. If you're not, LaForet, F*ret and Shibuya 109 will either cause your credit card to spontaneously combust, or provide you with an entertaining freak show free of charge.
When you're travelling around Tokyo, JR (or any other surface railway) is usually cheaper than the subway, and using the subway is usually cheaper than using a combination of the two.
You don't need to tip for anything.
A lot of people recommend getting a Japan rail pass. It's very good for what it is, but you have to travel a hell of a lot to get your money's worth out of it. If, say, you want to see the whole country in three weeks, it's a good idea. If you want to make a couple of middle-distance excursions and use it to commute the rest of the time, it's not. Getting the Shinkansen without one is very expensive, though, so consider other means of transportation - Tokyo to Kyoto is far cheaper if you take an overnight bus, and you can get to many places faster and cheaper than the train by renting a car.
Another alternative to the rail pass is the Seishun 18 ticket. It won't get you onto Shinkansens or express trains, but it'll give you five days (any five days you like, not necessarily consecutive) of unlimited travel on JR local and rapid services at certain times of the year. Not the ideal choice if you're short on time, since it'll take you a while to get anywhere, but it's a fraction of the price of a rail pass - Y10,000 compared to Y30,000 for a 7-day rail pass - and it'll get you anywhere if you don't mind the leisurely pace. Bring a book, look out the window, it'll be nice.
I can't think of anything else right now.