A good way to realise you’re dreaming is to look for “dream tells”, which vary from person to person but often include: text being hard to read, clocks showing the wrong time, mirrors not working quite right, not being able to remember how you got where you are, things changing appearance when you look away and look back, that sort of thing.

Unless you’re well practiced with lucid dreaming, you probably won’t be able to exert direct control—either your efforts simply won’t work, or you’ll wake yourself up. A useful technique I use is to think something along the lines of “Oh, of course this is what will happen next” and it often does—the structure of the dream is often driven by your expectations and beliefs of how things ought to operate. Poke around and try stuff to see what works for you! :)