The best thing to do is to repeat one word or phrase to your budgie several times throughout the day.
Use the same inflection each time.
I had a budgie when I was growing up that said a great many phrases.
Just a small sample included: Hello!; You're a cute baby bird; Wanta Cheeseburger?; Sweetie is a pretty bird. etc.
When I got my budgie Skipper (whom I still have) I taught him to say several phrases as well.
He loved to say "Whatcha doin'?" "Hi, Skippooter"
"Skipper is a cute baby bird", "Where's Scooter?" and several other phrases.
However, once I started adding multiple budgies to the flock and there were more than three, Skipper decided he'd much prefer to revert back to speaking only "budgie talk".
Once in a great while he'll sneak in "you're cute!" but generally now he only speaks "budgie".
You can start working with teaching your budgie words as soon as you get him or her.
Some budgies are very receptive to mimicking human speech while others have no interest whatsoever.