Have cruised solo about 20 times, with one coming up next month. The first time, I was terrified! "What the hell have I done? I'm going to South America, I don't know anyone, etc." Then I realized all the closet space was mine, all the drawers were mine, the bathroom was all mine - the selfish gene kicked in. I changed my clothes, walked out the door and never looked back.
First of all, you cannot be shy. I've been very lucky hooking up with couples or groups. I always ask for a table of 6-8 for dinner - they become "family". Participate in games, water sports, Name that Tune, things like that. You might have to approach a group and ask if they need another person for their team - people are almost always gracious.
Usually, the first time I visit a port, I will take a ship sponsored tour of the place - not a whole day thing but a 3-4 hour jaunt to get the feel of the land. You meet people on the tour and can ask what they are doing the next port - I've hooked up with lots of people this way and shared cabs, lunches and excursions cheaper than the cruise line.
It's funny but sometimes people are more open to talking to a single woman than to another couple or 2 women - if you're with someone else, you appear to be already "partnered", but when alone, you can find some interesting people. If you're sitting at a lunch table on the Lido and there's room for others, invite people walking by with their trays to join you.
Like all things in life, cruising would be much better with a loving man at your side to share things with, but, since I figure he's not coming soon, I need to get to places only cruising can get me - how else would I have seen The Panama Canal, Angel Falls, almost all of the Caribbean islands, swam with the dolphins in Honduras (last November), done a few trans-Atlantic cruises and seen the Mediterranean?
Yes, I've been on cruises that seemed like "Noah's Ark" - everyone coupled and watching people dance is not as much fun as dancing, but you can still enjoy a comedy or magic show by yourself - people around you will laugh with you.
As Mark Twain said, "In 20 years, you will be more disappointed by the things you did not do than by the things you did do". Keep that in mind - keep your smile ready, banish your fears, and JUST DO IT, Kid!