Effective ways to enrich your active vocabulary?

I come across words like rectitude, like laudatory, like indigent, and being an experienced reader with a strong grasp on my native language, I know what they mean. They're words that I know.

But they're not words I think of when I'm writing.

I know a thesaurus is a great friend, but honestly, I can't picture Nabokov sitting there looking up synonyms, nor do I believe that it's a habit any aspiring writer should make heavy use of. It needs to be there implicitly, in your head, ready for use.

How can I stir up the cauldron of lexical memory and bring the many sunken ingredients to the surface?

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EDIT:

A comment below makes the argument that using uncommon words is essentially akin to bad writing; that it's unnecessary and the writer is generally better off using simpler language.

Oh. my. God. Have you ever read 1984?

Clarity is king. That is the number one rule of writing, absolutely. Writing is about communication, and communication is about clarity. Clarity is king. It is a common mistake by amateur writers to use words that inhibit clarity, to use words of great rarity with great frequency to such an extent that their sentences have more syllables than meaning.

THAT DOES NOT MEAN YOU SHOULD STOP AT THE LIMIT OF A HIGH SCHOOL VOCABULARY.

Is looking up words a bad thing? Is expanding your range of expression an outdated notion? Should I call the sky pink instead of fuchsia for fear that my readers won't understand?

While words like tergiversate might certainly have superior substitutes, why should I stop using any word I don't hear on a daily basis?

I'll say this: I go to an engineering school, and people here do not read at all. I mean, period. They literally don't like reading books.

And when I hear a comment like the one below, I think of the moments here like when I called someone shrewd, and they asked what that meant. And it makes me so sad.

And that's the future that we encourage by being afraid to encourage the use of a dictionary.

Lastly, from the comment below:

"Aren't there enough common words to make the writing dynamic without irritating the reader?"

My intended audience never has been and never will be those who are irritated by new words.

Answer

One method I like to use to remember new words, or at least words I'd like to use more often, is to write them into sentences. So I'll take a word I want to dredge out from the depths of my mind (or a dictionary) and write 10 sentences that use the word in various contexts.

It's easier to recall when you use it for yourself, in contexts you've constructed as opposed to copying someone else's (such as dictionary examples).

Write it out with pen and paper, too, as studies have shown that we tend to retain information better when we write as opposed to type.