I generally use a digital clock, some text, or a picture of some sort, whatever is at hand.
I also agree with waht r3m0t said, RC’s only work because you believe that they work.
ypm.
I dont think RCs just work because of placebo effects… My hands are always weird in dreams whether I believe I’m dreaming or not.
Counting fingers works great for me 
Counting fingers, it works every time.
My favourite is looking at my hand. I do it every time I get lucid.
Every time I do it it looks less wierd than the last, and the numb tickeling rush feeling I get from it decreases every time too.
The last few times, the hand looked so normal I had to count the fingers to make sure I was dreaming.
Siiw: then what am I supposed to do? I forgot, I’ll check. By the way I’m 14 and don’t have a workplace.
confused, the point isn’t whether you think you’re dreaming at the time, but whether you believe that they will work correctly whether you are in a dream or not.
ypm, I wouldn’t go to that extreme. But I think it certainly plays a large part. Perhaps everything for some bad RCs… 
Though the most effective, for me, is holding my nose, my favorite is looking at my hand. I’d only use it as a backup RC or else it looks normal. If I do use it after another one, it looks so weird…! It’s been discolored, I’ve had up to 10 extra fingers, my hand will look somewhat deformed but it feels really weird…