Sometimes, I have no knowledge about any specific work or matter in Islam. Then I perform that work according my own desire. For example, I know the rules of performing wudu. If I don't perform it according that specific rules then It includes in sin and my wudu would not be acceptable. Then if I don't know about any work, their rules/ sharia how to perform them and I perform them on my own then are they included in sin or not?
Firstly and obviously, you should do your best to find out what is haram, what is halal, and what is best practice in general. Having said that, both the Qur'an (al-Ahzaab 33:5) and Hadith make it clear that if someone does something out of ignorance, or does something incorrectly, but is well intentioned, then it is not a sin, and this includes not doing something that one should be doing. So in a sense, Allah, unlike the laws of the land allows ignorance as an excuse. That's a part of what makes him the most merciful, of course!