Even if you're good at spelling and can produce engaging, verbose writing, the chances are that you struggle sometimes with your grammar. This is nothing to be ashamed of. Since formal grammar was dropped from the education system in many areas, many people have found themselves struggling as adults. Some have been proactive about finding solutions. They have used grammar checkers and read grammar guides. Yet they still make mistakes with their grammar. Why is this?
The problem with grammar checkers is that they're usually designed with a particular type of writing in mind. Grammar guides may give the impression that it's easy to get the basics right, which is true if you're producing the kinds of writing likely to be required of you in a school environment, but you'll need more complex grammar skills to handle all the kinds of writing you may be asked to produce in adult life.
The rules of grammar are not as straightforward as they might at first seem. You'll need to know specific forms of grammar in order to undertake jobs like writing letters or producing industry reports. What's more, some of these grammar rules are undergoing a continual process of change. It can be difficult for the layman to keep up.
The only real way to make yourself adept at grammar is to take a course with a tutor who can answer your questions, and to keep up with the way grammar practices are developing within the field in which you work. Alternatively, if you want to make sure you're using the right grammar for a particular important job, take a look at the EditFast database, where you can hire a grammar expert to help.