How do I know if there are fish where I'm fishing?

[cutuzov]

Just to add to the great advices given. Weather is the major factor in fish feeding. Air pressure can make any great spot sluggish or not producing at all. Moon phase, temperature...you name it. Only way to "learn" the river is to go and try.
This time of year is really hot for carp. Google "hair rig" or watch this video tie it and try it. Disregard the fancy gear references, you will upgrade later if you like it. Good luck and feel free to come and brag