For many people and businesses, Twitter is about getting as much followers as you can. Well, it’s not: it’s about getting valuable followers but about following valuable Twitter users too.
It’s simple to use a software that allows you to find people based on keywords in their tweets, start following them and then hoping they will follow you too. Don’t do it.
It’s also easy to start tweeting and follow few people back. Should you follow everyone back? No. Because there are a lot of Twitter users following automatically or because they want to sell you stuff (if you want to buy it, then there is no problem, right?)