Ask HN: How to retain the knowledge of syntax

I am a self taught web developer, I have written a few full scale applications and fully understand OOP principles and MVC structures. I can write using Java, PHP, JS, and a few more to a good degree.

My problem is that when writing applications on my own I seem to find myself going back to specific syntax and constantly looking up methods I have used many times from either previous work or documentation in order to complete parts of code.

How would I go about better retaining the specific syntax/methods? Do I just need to continuously keep writing applications in order to memorize it, or should I have this in memory already and I am doing something wrong?