Don't write long

Six pages is roughly 1500-1800 words. Decide on a larger subject. Find a great deal of research. Do write in a succinct manner, but fill the pages with details, reasoning, and analysis. Do not think about it as a longer paper, however as a deeper paper, with a wider base of understanding to be displayed to your instructor.

Other than this, a 6 page paper is written the same way as a 2 page paper. The difference is that rather than creating a point in one paragraph, you might need to spell out the finer details in greater depth, with several paragraphs.

I propose making a summary or a brain map so that you can capture and organize your ideas on your native language before you begin writing.

Don't write long, fuzzy sentences, as that won't improve your grade. Don't be repetitive. A long essay needs more stuff, so do more research and do more considering the context and the meaning of the topic.