All deleted post are not only post that is spam or off-topic post in which what I thought before that posts that are deleted are only spam and off-topic reply and then I read a thread that has the same experience as me that there post are deleted. The reason why your posts are deleted are answered.
1.) Spam
2.) Off Topic/Out of Topic
3.) Considered as low quality post (which is not much important for people to know and decided to delete the post.
4.) Your posts are deleted because it is reported.
There is only one simple answer/solution avoiding your post being deleted or reported but you must learn first which it will take time before you can post high quality post and you should start at the basic first. The simple answer/solution to avoid your post being deleted is to post high quality, constructive post rather than posting non-sense, spam, off-topic post which is only a waste of time. There is here in this forum about what to do that will help you post constructive post. I'll mention some of the tips that I know in the thread I mention.
1.) Do not reply to a thread where you don't have knowledge about the topic that's been discussed.
2.) You must be knowledgeable so you will be able to join the discussion and share what you know about the topic that most people didn't know.
3.) Learning the things you don't know by searching, reading and scanning.