I love to cruise solo (when DH or kids can't go) and have sailed solo over a half-dozen times in the last 6 years.
What cruise line are you going on? Most have a "singles meet" early on, usually the second day. On my first solo cruise I went and there was one other woman and no one from the cruise staff showed up. The other woman and I chatted, had a drink and it was nice to know there was another solo woman on board. On my other solo cruises I didn't bother to go to the singles meetings.
Mostly meeting others is simply about being open, friendly and fun. The first way to meet people is to do traditional dining and sign up for a large table. I've met some really wonderful people that way. The second way is to get involved in activities. I join others for name that tune or other shipboard activities, it can be really fun and a great way to meet people. Excursions are also a great way to meet other passengers. More often than not once I've shared a great excursion with people we meet up for lunch, drinks or arrange to be on other excursions together.
As a woman solo traveler I have found people will "adopt" me, include me in their activities, get togethers, etc. They also keep an eye out for other solo travelers so we can meet each other.
On a cruise two years ago I was just so happy to be there I was smiling all the time and would laugh out loud--sort of sounds crazy, I know, but being that happy draws people to you. People would walk up and say "You are having so much fun!" and want to join me.
There are a few drawbacks to being a woman solo traveler, some people think you couldn't find anyone to go with you and pity you openly, sometimes other women think you are after their man or, the truly dreaded, you are there to meet men! There is nothing you can do about the first but the last two are easily dealt with by speaking about your DH and kids (if you have them) early on.
The best part of solo cruising is you get the tiny cabin bathroom all to yourself
Let me know if you have any other questions.