There is no shortcut for learning grammatically correct English. It takes time to understand and put to use the rules of English grammar. just you should start learning with proper way. Here is the way...

Tense:

Start with working on the tense. Tense dictates the verb. It defines the timeline of action. You have to memorize the verb forms. Truth is we do not use all the tenses in spoken English. Interact with good English speakers to get the hang of which of the tenses are actually used.

Common Pronoun usage He/Him, She/Her, They/Them, We/Us, I/Me

I, He, she, they and we are subject pronouns. When the subject is doing the action you use these pronouns. Example: I spoke to her.

Me, him, her, them and us are object pronouns. These pronouns do not do an action. They simply receive an action. Example: Give it to me.

Never start a sentence with me. If there are two or more people involved, always start with other people’s name and end with referring you as ‘I’. Example: Raj, Sanvi and I went to a movie.

Voice

Active voice is simple to frame and speak. Active voice has a subject as the doer of the action.

Remember that whenever you change a sentence from active to passive voice, the subject and the object swap. And if that involves the pronouns, they will swap to their relative object or subject pronoun form.

Example: Wrong: The movie was gone to by Raj, Sanvi and me.

Right: The movie was watched by Raj, Sanvi and me.

Prepositions

Preposition brings out the relationship of an object to its surroundings. Preposition is always followed by the object of the sentence. So first the P and then the O.

Strictly speaking, you should never end a sentence in preposition. But spoken English is very forgiving in that regard.

Few other miscellaneous tips

Questions tags are always opposite in sense to the question. If the question is positive, the tag will be negative.

Example: You didn’t do it, did you?

He came last night, didn’t he?

‘Does’ is answered by ‘s’ in the verb form. ‘Does’ is used for singular. ‘Do’ is answered by the present tense of the verb and is used for plural.

Examples:

What does he do? He teaches.

What do they do? They dance.

The machine does the drying by spinning.

The machines do the drying by spinning.

These tips are just guidelines and not mathematical formulas where substituting one verb with another gives a new sentence. These rules are purely for understanding. Listening to native English is one of the proven ways to improve your grammar and spoken English.