“The” is a very common word, and a good word to practice. Read some text, and focus on “the.” To make “the” sound good, it alway needs to be said slowly. “Th” in any word will sound better if you let it have some time. Also, the vowel in “the” is the most common sound in American English, and in “the” it is a very long sound. So practicing “the” will help you get used to making vowels long.
Usually the vowel in “the” is the same as in “hut”, “luck”, and “but”. If “the” is before a word that starts with a vowel sound, the vowel in “the” is the same as in “heat”, “feel”, and “feet”. Here’s more about that vowel. Both these vowel sounds need to be long; the longer you make them, the more American you will sound.
Here’s some random text to use for practice: https://simple.wikipedia.org/wiki/Archosaur