Build a small two frame box and put a frame of brood and a frame of honey in it. You can go mess with this anytime and look for the queen knowing she's only likely to be on the one frame of brood. After finding a queen every night for a week, you'll be much better at it. :) Or set up an observation hive with an unmarked queen so you can practice every night finding her.
Next time you try to find a queen and try using these tricks to find her:
The queen is usually on the frame of the brood chamber that has the most bees. This isn't always true, but if you start on that frame and work your way from there you will find her either on that frame or the next 90% of the time.
Of course the obvious thing is that the queen is larger, but that isn't always easy to see when there are bees climbing all over her. Look for the larger "shoulders" The width of her back, that little bare patch on the thorax. These are all larger and often you get a peek at them under the other bees.
Don't count on your marked queen still being there and being marked. Remember they may have swarmed and you didn't catch it or they may have superceded and she may be gone.
Look at how the bees act around the queen. Often there are several, not all, but serveral bees facing her. The bees around the queen act different. If you watch them everytime you find a queen you'll start noticing how they act, and how they move different around her. Look for circles of bees. Often they are feeding on some broken comb, but sometimes there is a queen in the middle of them.
The queen moves differently. Other bees are either moving quickly or just hanging and not moving. The workers move like they're listening to Aerosmith. The queen moves like she's listening to Schuber or Brahms. She moves slowly and gracefully. It's like she's waltzing and the workers are doing the bossanova. Even if she's in a hurry she lumbers more than runs. Next time you spot the queen notice how the bees in general move, how the bees around her move and how she moves.
Also the bees tend to get out of her way when she moves. Look for movement where the bees are clearing a path.
Usually the queen is slightly different color. I have not found this helpful because she's also usually close enough in color that she's still hard to spot by this. The worker bees usually have disticnt stripes, the queen usually doesn't (sometimes she does but usually she doesn't).
Another trick is to put an excluder between every box and come back in four or five days. The box with eggs in it has the queen in it.
Usually I don't smoke them if I want' to find a queen because she tends to run and then you don't know if she'll be in the usual spots like in the brood nest or on a frame with fresh eggs. But another trick is to smoke the bottom heavily and then set the top box off and look for her there. Or smoke the top heavily as you remove boxes until you get to the bottom and she will probably be there. She runs from smoke more than the workers do.
Of course you should mark the queen so you know how old she is. Get a color for next year (White would be next years color right now) and use it on drones to practice catching and marking them. Buy the color for this year for actually marking the queen. That way you don't get the marked drones confused with the queen. The drones will be gone by next year and you'll already have the marking pen for that year.