To reach the max level in the Secret Agent career path you will need 10 Logic and 8 Charisma for the Diamond agent branch and 10 Logic and 6 Mischief for the Villain branch.
The Villain branch has an extra promotion so I would personally go for the Diamond one, you also earn almost double per day.
If you need an easy way to level your skills, logic can be done through the chess board which also gives you to Focused moodlet which will help with promotion.
Charisma can be levelled through talking to other sims or more consistently through practising speeches in the mirror.
Mischief can be done through the social branch on other sims, once you reach level 2 I would recommend 'Trolling Teh Forums' as it is a constant flow of experience.
If anyone has anything to add please comment.