You can buy followers, but quality always is very bad and in this way you can destroy your Twitter account.
Then why are you even suggesting this option if you know that this is totally stupid move? Plus, Op said that he don't want want to paid for it.
I read this thread and so far Ardenyham gave us the best tips. I agree with him completely.
Some of my tips:
1. Remember that social media positioning (this is what you will be doing) is not exactly free - you will have to waste a lot of time on this.
If you don't have time or patience for this, then you may already give up.
2. Create solid account, with good detailed profile, picture, don't use some random picture as you profile photo.
3. Actually compose interesting, serious, funny or informative tweets - depends on what is you niche. If 90% of your tweets will be promo offers or affiliate links you won't get any followers.
4. Post interesting links, pictures, videos.
5. Tweet as much as you can, but don't spam with zero content tweets. Take into account your time zone (or time zone you are aiming for). Don't post tweets when people are asleep.
6. USE HASHTAGS! I mean it, a lot.
7. Follow everyone who follows you. You have to remember about this - especially when you are starting.
8. Share your twitter with everyone, in your signature on bitcointalk, have it as your messenger status etc.