It's actually easy for even amateurs to link writing styles if the target has some unique patterns or quirks in their style. A few people on this forum have been linked, such as mtljohn and Chaosforpeace. The best thing you can do is spell correctly and use proper grammar. Make your writing style as normal as possible. There's a tool called Anonymouth that's supposed to help you write more anonymously by analyzing your writing and identifying words and phrases with low frequency, or that are unique to you, but it's hard to use and extremely buggy.