I'm a Japanese. About the stations and airports, I'm sure you'll find the way. You can find the English signs and if you ask people, they will help you, even they don't speak English. I'm sure Japan is one of the safest countries, so no problem you can travel yourself. 

If you're traveling for a long time, I recommend you to try JRail Pass which allows you to go from north to south. We have different attractions from place to place. You may have problems about the language if you go outside the cities though. But you can find the beautiful things there too :)

Enjoy your traveling in Japan!

Airports are full of English signs and people who speak English. Subway stations in Tokyo are also easily accessible for English speakers. If you travel outside of Tokyo, you may have more difficulty. 

Don't worry too much about solo travelling in Japan. I have done it once and I have a female acquaintance who also recently travelled to Japan solo.
Generally, when asking for help in Japan, if you feel that you can't really express in Japanese, try seeking help in this order:
1. Older women
2. University women
3. High school girls
4. University guys
5. High school boys
6. Older men
Most women have a higher tendancy of being able to understand English(but its just a rough guide)

Depending on how far you going to travel, you might want to get Japan Rail Pass if you are covering more than 2 areas. The rail pass covers the basic shinkansen rides, JR lines and some of the bus rides in Tokyo and also some midnight buses. The rail pass has both the normal version as well as the green car version. Generally, the normal version would suffice.

Sights and attractions, really depends on where are you going to and what kind of attractions are you looking out for.
Tokyo wise:
Shibuya - Shopping district with the very famous Shibuya crossing where some of the seasonal events are held
Odaiba - This is the place where the famed gundam statue is and also where Disneyland is located.
Osaka wise:
Universal Studios Japan - other than the famous spiderman ride, Jaws, Ride Into the Future, and Harry Potter attraction(Note: for Harry Potter attraction, you need to get a queue ticket for it), USJ also have 2 new attractions coming up next year Jan till June if I'm not wrong on that.
Dotonbori - The place where most food delicacies are located at. Takoyaki and theres also grilled crab which tasted awesome.
Umeda Sky Building - This is where you can see the cityline of Osaka and its a famous spot for couples during the evening-night time.

I would say, don't worry too much and just boldly travel to Japan. It will be a wonderful experience! I would say more but the character limit :/

Japanese people are very helpful, and there are many signs in English. Also, Japan is one of the safest place on earth these days.

Get a rail pass before you leave - can be purcased at a Japanese travel agency.  note you must purcase the pass outside of Japan.  Then you can use it on all the trains, bypassing the turnstiles etc.

There are many places to see in Tokyo.  You can use the rail pass to visit Kyoto by bullet train.  Highly recomended.

I've been to Tokyo in 2010. It was difficult to find somebody who could communicate in English. I only met 2 japaneses who spoke English fluently and it turned out they both used to study abroad. The good news is there are many native English people living there. So you don't need to worry about it.