Follow these guidelines and you won't go far wrong.
http://www.abta.com/consumer-services/travel_p roblems.
when you write to them, bullet point you list of complaints. No company want's to read a long monologue.
Don't demand and expect a full refund- you most definitly won't recieve that. Be realistic with what you'd expect as compensation. For example, the cost of your flight would have been about 75% of youir holiday costs, to to expect a full refund because the hotel was a mess is un-realistic and won't even be contemplated by any holiday company.
Lastly- good luck, be persistant, but above all don't threaten, unless you REALLY know what you're talking about and try to keep level headed about it.