In the rule-oriented world of grammar, the process of converting a verb to a noun is a very specific process called nominalization. There's no single rule for converting a verb to a noun, and some verbs can't easily be converted. In many cases, however, simply altering the suffix can convert the verb to a noun. Additional options for converting a verb to a noun include adding an article or possessive.
You should only convert a noun to a verb when it serves the goals of clarity and precise language. For example, it's much easier to say, "the leader" than say, "the person who led us." But other times, conversion might not work as well. For example, if you're describing an alcoholic, describing the person as a drinker might provide less information than simply referring to him as an alcoholic or saying he likes to drink alcohol.
Adding a Suffix
Many suffixes can be added to verbs to change them to nouns. Examples include adding -er as in runner, adding -tion as in action or adding -ade as in blockade. You might also use -ment as in merriment or -ant as it's used in defendant. Check a dictionary to determine whether the suffix you're adding constitutes a real word. If it doesn't, you'll need to find a way to convey your meaning without converting a verb to a noun through the addition of a suffix like -er, -tion, -ade, -ment or -ant.
Adding an Article
Some verbs can be used as nouns without altering the word, and adding an article such as "the," "an" or "a" can make it clear you're using the word as a noun instead of a verb. For example, you might write, "The man prepared for the jump." Sometimes you'll do this even when you've converted the verb to a noun earlier in the sentence. For example, "The runner prepared for a run" makes it clear that you are using run as a noun instead of a verb.
Adding a Possessive
Just as when you add an article before a word, adding a possessive adjective such as "her" or "his" can clearly differentiate verbs from nouns. You might write, for example, "The students enjoyed reading the writer's work." Another example might include a sentence such as, "The old woman was excited to take her daily walk." When using an apostrophe, be careful it is used correctly when adding the possessive of the word.