How to make my intention and actions exclusively for Allah?

Dear sister, you are most welcomed in (Al Alukah) website. We were delighted with your massage which gives us reassurance that the nation of Muhammad (peace be upon him) is still in good condition with your presence and the presence of good girls like you.

I want to comment on your question in the following points:
First, your concern about intention and sincerity is a proof on the presence of faith in your heart. The pious Predecessors (may Allah be pleased with them) used to busy themselves with devoting intentions and action to Allah (may He be Glorified and Exalted). This is a good sign, so thank Allah for it.

Second, Sincerity of intention does not come off-hand, but intention needs to be maintained through the close observation to it and to the actions and sayings that accompany it, no matter how tiny are they, then making sure of sincerity before doing any action. You should filter your intention from the impurities of oneself (such as fame, nice praise, material gains, and so on.) If offering Salah is an action, devoting intention is also an action.

Third, from the clear signs of devotion in any action is not to be affected by people's praise or dispraise. It is true that we are human and we feel delighted when we hear people's praise and be affected when we hear their dispraise, but taking that as the main motive is a dangerous sign.

Fourth, there are important and dangerous moments that you should take into consideration; which are the moments when the people see your work and praise it. In these important moments, be careful of the feelings of arrogance and vanity, and praise Allah for guidance and success for all these are from Him alone. Ask Allah to accept your deeds and seek refuge with Allah from the rejection of your work. Do not fear or panic because such questions were raised during the Prophet's lifetime and his Companions asked about them. It was reported in Sahih Muslim that the Messenger of Allah (peace be upon him) was asked: What is your opinion about the person who has done good deeds and the people praise him? He said: "It is glad tidings for a believer (which he has received in this mortal world)."  This is the glad tidings because a person did not do that work for people to see him, but he did it for the sake of Allah and Allah made the people see it to praise his action, unlike the people who do something in order that the people praise them for what they did.

Finally:

it is well-known that the matter is not that easy, but when Allah (may He be Glorified and Exalted) finds that the effort you exert in devoting the intention to Him is sincere, He will help you (by His Will) and accept your action by His Mercy because He is the Most Generous and the Most Merciful.

May Allah grant you success, and do not forget to supplicate Allah for us.

You are always most welcomed in Al Alukah website.