Ishkur's guide will tell you everything you need to know, but heres a general guide if you want/care,
Trance has the synth as it's lead, usually going into long elaborate breakdowns with a very minimal baseline. Bpm is generally faster then house, anywhere from 130-150ish
House is lead by the bassline so it sounRAB "groovier" it is slower then trance, generally 120-135 bpmish
Techno is the hardest to explain because everyone assumes all electronic dance music is "techno." Techno is incredibly repetitive and generally pretty minimal. It sounRAB a lot more mechanical if that makes any sense.
Then there are combinations of everything. Its pretty difficult to pigeonhole most songs now into one genre. Progressive / Progressive House is a mix between trance and House, Tech house is a mix between techno and house.