The first and foremost ting before joining a bounty is to increase your knowledge about cryptocurrencies in general. Make sure you know about them so as not to post any spam posts on the forum. You must increase your English skills because posters with low quality of english are often not selected for bounty campaigns.
Make sure not to just post some rubbish for the sake meeting the bounty's post requirements, it would make the forum a mess and refrain from posting in mega-spam threads.
If you keep all that in mind, your post quality would definitely improve, and you would be selected for bounty campaigns.