There is a New Yorker cartoon from early in the internet era. It shows two men in medieval dress and setting. One is showing a large folio book to the other, who responds, "It's a great invention, but it will never replace the scroll."

The book did more than replace the scroll. With the advent of printing it replaced the Art of Memory. When books were expensive and relatively rare people had techniques for remembering whole volumes. With the development of printing and the mass production of books people forgot how to remember. There was no need. They could look it up.

Mneumonics are memory devices, techniques for remembering. I first learned about them in medical school where there were vast amounts of information to remember and you couldn't use your books during tests.

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Being able to conjugate a verb is essential. You have to be able to say who is doing the action and when. It is a large step towards fluency. Many is the time I remember the look of confusion on my listener's face when I said "I did it" instead of "you did it" or "she did it."

I say "master 90% of the past tense in 5 minutes" because 90% of the time you are speaking in the singular: I, you, he, she, not in the plural: we, they, you. Don't worry about usted/you formal. Right now it is an unnecessary adornment. You are just trying to make yourself understood. My approach is down and dirty, street-level.

Let's start simple: tomar = take.
I'm assuming you already know the present tense.

Present
tomo = I take
tomas = you take
toma = he/she takes
(Toma is also the simplest/informal command, take; tomalo = take it. Keep it simple, don't worry about the formal command.)

Past
tomé = I took
tomaste = you took
tomó = he/she took

Ok, here come the mneumonics.

Tomó = he/she took is almost the same as tomo = I take except there is that accent. (To sound the accent put stress on the o, that is, say it louder.)
The third person past is the same as the first person present except for that accent.

(-er verbs third person past end in ió; comer; he/she ate = comió. There's that accent again.)

Tomé = I took is easy to remember because the e is all we have left; we've already used tomo and toma and tomó.

(-er verbs first person past end in í; comer; I ate = comí, because we've already used como = I eat and come = he/she eat. There's that accent again.)

Tomaste = you took
Te is a way of saying you. You already know the present tense tomas = you take. Just add te to to the present tense, tomas, to make the past tense, tomaste = you took. Add you (te) to you take to make you took. Get it?

(-er verbs work the same way except -es becomes -is; comes = you eat becomes comiste = you ate.)

The Art of Memory involved visualization. Look at the present and past tenses in the gray boxes above. If you see the pattern, you will automatically remember the details. Tomo goes from position one in present to position three in past. Tomas in the present becomes tomaste in the past; just add te (you).

Yes, this is past preterite. Yes, there is also past imperfect. Don't go there, yet. When you get the fundamentals, learning becomes fun. The reward of being able to make yourself understood, lightens the process of learning. Then you can work on the details and your style and enjoy doing it.