make sure it is more than 100 characters and don't be off topic from the questions answered.
not from the length of the character. try to reply according to the topic of the thread. no need to repeat reviews that have actually been answered by previous people. it will make the post will tend to be ignored.
more reading of the thread in its entirety before finally starting to reply. and of course, just focus on topics that you really master. if you want to seek new knowledge, simply first read the existing information. ask questions if something is not understood.