To get real follower who will be productive, create original content. don't go for those like or follower exchange
hello, just use service that help to follow a mass of people and those people will follow you back. but it is not target so if you just want volume do that and it' free just your time. but if your purpose is to have targeted people just do the hard work.
Gisa, unfortunately, you can't get big number (for instance 50000) of twitter followers free and quickly( Free and quickly you can do it only with the help of paid service.
all that is free, you will need to pay. I think a good advice is to subscribe to groups on your topic and add friends from there, people will be added to you themselves If you are active in groups.