What ambition should I aspire towards in my life?

Be a da'ee! There's nothing greater than it! You can be a faqih or an alim but that doesn't automatically make you a da'ee! Doing ta'leem is not da'wah. Writing a book, even on the subject of da'wah, is not da'wah! Knowing a lot or acquiring ijazat after ijazat makes you educated and not a da'ee! For daw'ah is the act of inclining, convincing and encouraging others to the truth of Islam. Allah says, "Invite in the way of your Lord with wisdom, goodly exhortation and debate them in the best manner" [16:125]; "say, 'This is my way, I invite unto Allah with sure knowledge (baseerah)..." [12:108]; "unto this invite and stand firm (istiqam)..." [42:15] The da'ee is a faqih in the aspect of da'wah for he is not permitted to undertake it without knowing the fiqh (rules) of it! And he is also an 'alim in this field for he must have knowledge (ilm) as he/she is not permitted to invite to what he/she does not posses! It doesn't mean he has to study and learn for years. It is sufficient for him to carry however much he knows for Imam Bukhari (rh) in his Sahih that Rasulullah (sallal Allahu alayhi wa-sallam) said, "Convey from me [even if it's] one ayah" It is the da'wah that gives life and it is of the best of actions! Allah (subhana wa ta'ala) says, "O you who have believed, respond to Allah and to the Messenger when he calls you to that which gives you life" [8:24]; "And who is better in speech than he who invites (men) to Allah..." [41:33] Imam Ibn al-Qayyum al Jawziyyah (rh) said, "The du'at (callers to Allah) who are exclusive to Him, are those who call to His Deen, His worship, Knowledge of Him and to the Love for Him. These are the exclusive ones from among the creation of Allah and the best in status with Allah and the highest in value and rank." [muftah dar as-sa'adah]