What is better: One big SQL query or several?

Hi, I have relational database and I want to make the most of the data across several tables; for example, a table with sales data and the table with the prices, and another table linking both; I wonder if I want to display that data, and adding counting the data, or any other info I can get from the tables, what’s the best way to do it: build a big fat messy query or several queries, each one depending on the previous one? I don’t want the site to get sloppy