It is . . . . . . . . good practice to help . . . . . . . . poor and needy.

The first blank will take 'a' because 'good practice' is used in a general statement.
In the second blank, the words, 'poor' and 'needy' are adjectives. However, they are also sometimes used as nouns to refer to the entire class of people who are 'poor' and 'needy' respectively. Hence, the definite article, 'the' is used before both these nouns.