Hmm what do you want?A definition or an example?
Per definition a good deck is defined by winning often (pretty lame and circular yeah).But I can`t think of any other way to describe it.
Good is normally relative to the meta of the tournament/environment.(so to say when you know that Deck A will be played by 90% of the field, and Deck B got a 70% win percentage against Deck A then Deck B would be a good deck for that tournament/environment.)
But even though I said that being a good deck is relative in magic rather than objective most of the decks played in a tournament will have an overwhelming win percentage vs mill.I hope you get what I am trying to say.If not please let me know so I can rephrase myself.
For an examples just look some winning decks up at starcitygames I guess.You can summarize all the Decks into 3 very broad categorize.
Aggro, Control and Combo.
Aggro will generally try to kill the opponent with their animals and use their spells to kill the animals of the opponent or to burn.Here you can separate into fast aggro and mid range aggro(very general and inexact.Examples: Goyfsligh,Zoo,Boros)
Control will generally try to stall the game and eventually win someway later.Here you can separate into "Draw-go" and "Tap out" control.Draw-go will mostly play instants,counter your stuff and draw cards in your end of turn.Thats why "draw go" because their turn will most likely look like that.They will draw a card and say go.Tap our is more proactive in that it tries to just flood the board with better stuff than you.(Examples:Mono-U control,Esperblade,ubg loam control,solar flare)
Combo will just try to play unfair and win through some combos(duh).Here you can separate into fastcombo which just ignores the opponent mostly (belcher,dredge) and slow combo which tries a more solid approach.(high tide,the epic storm)
And finally there are obv the hybrids between the 3 MAIN archetypes like aggro-control,combo-control and aggro-combo.
Just to give you an overview what generally is perceived as a good deck(though they must not necessary be a good choice)
Maybe that was too much now,if so I am sorry.