Lelouch's Geass isn't a OPed power that grants wishes
Lelouch's Geass, bestowed upon him by C.C., gives him "The Power of Absolute Obedience", allowing him to plant commands within a person's mind upon eye contact in a manner comparable to hypnosis.
- The victim will not perform any action disallowed by their physical or mental capabilities, though they will try to carry out the command to the best of their ability. For example, a victim will not be able to correctly answer a question they don't know the answer to, but will direct the user to someone who can if they are able.
Source: Lelouch vi Britannia > Abilities > Geass
so even if Lelouch used his Geass on himself to "Achieve all your goals" it wont just magically make it happen. it only seems like that with Suzaku and Euphemia because
in Suzaku's case he was more or less suicidal as a means to atone for his past. Lelouch's command to "live" just forced Suzaku to not do anything that would needlessly throw away his life (ie. stand in the line of Hadron Cannon fire just to ensure Zero was killed)
in Euphie's case it override her own will of not wanting to kill the Japanese and in the end she didn't kill all the Japanese
A "Achieve all your goals" is also very dangerous as since as shown with Suzaku and Euphie it overrides one's wills it would also override morality. consider that one of Lelouch's goals was to get revenge against the Britannian Imperial Family and killed Clovis to this goal. now even if we assume Lelouch wouldn't harm Nunnally (who is in the royal family) a geass command to achieve all goals could just have him just take a nuke he finds to Pendragon and detonate it when the entire royal family is gathered there along with millions of innocent people.
we see this more or less happen in Season 2 when Suzaku detonates the F.L.E.I.J.A. at the start he doesn't want to do it and Lelouch would have successfully called his bluff when Suzaku threatened to detonate it during the second battle of Tokyo, however while he was prepared to die as a form of atonement during the fight the Geass order from Lelouch to "live" activated and forced Suzaku to kill millions of people just to save his life.