What is the outcome of Salatul Istikhara, and is what one does after Salatul Istikhara the best?

Istikhara is a servant's request to their Lord to choose for them the best of matters. If one performs Istikhara, they should proceed with what they deem most beneficial, for if it is good, Allah will decree it for them, and if not, He will avert it from them. The benefit might lie in something you perceive as bad, as Allah Almighty said: "And perhaps you dislike a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah Knows, while you know not" (Al-Baqarah: 216).

Istikhara should be performed in all matters, as the Prophet, peace and blessings be upon him, taught his companions. Then, the one performing Istikhara should proceed with what they intended. If it is facilitated, then it is good; otherwise, the benefit was not in it.

After Istikhara, entrust your matter to your Lord and rely upon Him. If your heart finds ease in one of the two matters after detaching from personal desires, then proceed with reliance. The most important thing is the presence of the heart during supplication and sincerity in seeking refuge with Allah, for Allah does not answer the supplication of an unmindful heart.