Use "Foolish Burial" to send strong Dragon(s) to the graveyard before this card is summoned onto the field. Use one of the tactics below to make sure your opponent attacks "Decoy Dragon", and you will get the monster you sent to the graveyard to the field.
Since the opponent is unlikely to voluntarily declare an attack against this card, this card can be used to stall like "Marshmallon". Even if they do declare an attack upon it and manage to destroy the summoned Dragon by battle, "Decoy Dragon" can simply summon the dragon from the Graveyard again the same turn, perpetually preventing itself from being attacked.
Use "Staunch Defender" in combination with "Decoy Dragon" and a monster such as "Spirit of the Breeze", "Dancing Fairy" or "Medusa Worm" which aids you significantly so long as it stays on the field, but can easily be destroyed. If/when your opponent decides to attack the bait, then you can activate "Staunch Defender" and summon a high level dragon, and then on your turn go on the offensive.
You can combine this card's effect with "Magic Cylinder", your opponent will take damage and you can Special Summon a level 7 or higher Dragon.
If you have "Tyrant Dragon" in your Graveyard, and "Decoy Dragon" is your only monster out on the field, use "Battle Mania". You can Special Summon "Tyrant Dragon" by tributing "Decoy Dragon"; your opponent will have to attack "Tyrant Dragon".
Use this card to special summon "Hieratic Seal of the Sun Dragon Overlord" when this card is attacked. That target will almost assuredly be destroyed in battle, therefore securing a permanent battle lock. The only way your opponent's would not destroy the target would be if they attack with a monster with 0 ATK.
You may use the effect of "Decoy Dragon" to Special Summon a Level 7 Dragon, then use "Metamorphosis" to bring a "King Dragun" and Special Summon a high-level Dragon, then you get 2 beatsticks in a shot.