1.)Not seeing the long-term outcome of his actions
Fett makes a clone army using his template, knowing that it is for the Republic and would be used against the Seperatists. So what does he do? Becomes a bodyguard for Dooku, leader of the Seperatists? Smart move, buddy. Had he lived to see the Battle of Genosis, chances are he would've been gunned down by the armyhehelped create.
2.)The Rumble in the Rain
So Fett sees the Slave 1 coming about, guns rotating towards Obi-Wan, and he fires his missle? Wouldn't it have been smarter to wait until the lasers fired, and Obi-Wan was down to attack him? This is forgivable, but his next mistake makes zero sense.
Obi-Wan has just been blasted all to hell by missles and lasers, Fett has an advantage that A.) Kenobi may still be recovering, and B.) He still is out of Obi-Wans range. So, disregarding all common sense, he flysright downto Obi-Wan so he can kick him? Thats right he decided to do this instead of just standing up on the platform shooting at the tusseled up Obi-Wan.
Obi-Wan reaches for his lightsaber and Fett grapples his arms together with his whip-chord. So instead of actually shooting his carptured prey (his flamethrower wasn't broken of anything), he flys around for a while until Obi-Wan reaches the pole.
3.)Geonosis Arena
Mace Windu has just been knocked down by the Reek. Perfect chance for Fett to shoot him with his missle or blasters from a distance at his defensless enemy. Nope, too easy. He flysright downto Windu (inspiring a bewildered look from Dooku also, he knew it was stupid too

There you have it folks. Jango Fett is a nitwit. His son Boba (through tales of the EU) seems to be much better at what he does, as his father inteneded it to be.