Rule 1. The presence of whoever or whomever indicates a dependent clause. Use whoever or whomeverto agree with the verb in that dependent clause, regardless of the rest of the sentence.

Examples:
Give it to whoever/whomever asks for it first.
He asks for it first. Therefore, whoever is correct.

We will hire whoever/whomever you recommend.
You recommend him. Therefore, whomever is correct.

We will hire whoever/whomever is most qualified.
He is most qualified. Therefore, whoever is correct.

Rule 2. When the entire whoever/whomever clause is the subject of the verb that follows the clause, look inside the clause to determine whether to use whoever or whomever.

Examples:
Whoever is elected will serve a four-year term.
Whoever is the subject of is elected. The clause whoever is elected is the subject of will serve.

Whomever you elect will serve a four-year term.
Whomever is the object of elect. Whomever you elect is the subject of will serve.

A word to the wise: Whomever is even more of a vogue word than whom. Many use it indiscriminately to sound cultured, figuring that no one will know any better.

Why should one learn grammar?

There are many such confusing words, phrases, rules etc in English. We cannot learn such rules in a day’s time. It is almost impossible to memorize all of them. An idea of such grammar rules come about when you have a stronghold in the language. Still, to refer from time to time and realize our errors, and correct them using such guides and resources is very important.

How many of us know what Antecedents are? They are the nouns replaced by pronouns. Still struggling with the usage of ‘I’ and ‘me’? The answers to all these questions will be solved once you learn the English grammar rules properly. Similarly, the objective case, commonly confused phrases, defining and non defining clauses, inverted sentences, irregular comparatives, superlatives, possessive pronouns etc also can be perfected following the English grammar rules