There's a reason so many of us like going out for drinks -- cocktails are just so much better when made by a professional bartender. Especially these days, when mixologists have made mixing drinks an artful endeavor. It's not that great cocktails can't be made with your own home bar, it's just that most people don't know what to do with those bottles in front of them (besides drink them, of course).
The principle behind mixing a drink is simple: you just pour together ingredients, stir and sip. But there are important details that cannot be overlooked for a cocktail to actually taste like something you want to drink. None of them are difficult, but all of them crucial.
If you're making the mistake of forgetting about the details, you're missing out on what could be a great cocktail. Don't waste another drink, read up on what not to do and enjoy better cocktails.