There is nothing hard about it. If you post meaningfull constructive posts, you can join some signature campaign which is currently open. You can find them listed in the Services section (https://bitcointalk.org/index.php?board=52.0). In simple explanation, you are paid for an advertisment, which you hold in your signature.
The best way is to try to learn about bitcoin, trading, mining or other topics here on the forum and during the learning process, talk about it. That's how your posts start to be constructive. It's important to not wildly spam forum threads, just to gain high number of posts, this can get you a permanent ban not only from sig campaigns, but also from the whole forum. And the last advice - ALWAYS read carefully the rules of the campaign.