Most cruise lines will seat solo cruisers together at a table. Select a specific dining time and not the anytime dinning. Ask to be placed at a large table. A table of 8 singles makes for good conversation and a great way to meet other singles. Also they usually have a singles meet/party on either the 1st or 2nd night. I see a lot of posts where someone says "my husband and I are going on a cruise and taking my sister. Do you think she will have fun and be able to meet other singles." There are lots of singles that go on cruise, some go alone and others go with friends or relatives. You would be surprised at how many there are.
Like CruiseSC said: Get there early and get a spot where you can watch the boarding and pictures. Don't only look for the singles but look for the 'groups with singles'. You know what I mean, a group with one or more singles in them. They are easy enough to spot.
Go for it. Have fun and enjoy your cruise.