DO think of an original idea. This is the most obvious. Copying a pasta will likely have it removed. Think of something not many people have done.
DO read other pastas for a general idea of what people like. Don't know whether or not your pasta is funny? Read generally loved pastas for a general idea of the wiki's sense of humor.
However, DON'T use one joke as a reference. This will make your pastas get stale and most of them will get deleted, or at best, a ton of groans.
DO write satire. That's what Trollpastas are; satire of normal creepypastas. Writing satire will give a true meaning to Trollpastas.
DO keep a good knowledge of categories. The amount of uncategorized pages is staggering. Putting in categories will attract people. The more categories you add, the more likely someone will read it. However, you need to understand how the many categories work. We have the Genre Listing for that.
DON'T think just because it's bad, it's funny. This is they key rule to writing a good trollpasta. If it's an unreadable mess of caps and EVIL PATRIXXX, it's not funny. You can make it ALL CAPS, have very bad grammar, or have EVIL PATRIXXX, but don't exaggerate it. ZOMG IZ ZGARIEZED BAZDA LIGE 1337 H4X is a primary example of how not to obey this rule.
DON'T plagiarize. I think it's a lot more important than the above rule, but eh. Taking The Tale of Shrek, replacing everything related to Shrek with... what say... Spy from TF2, and not doing anything else is not funny. If you're gonna make a blatant ripoff, at least add some original content. For example, if you're gonna rip off Sonic.exe, add some more content.
DON'T spam. This is why the One sentence category is generally frowned upon by the admins. Don't spit out short, unfunny and unoriginal pastas out at rapid speed. This is called pointsgaming, and is frowned upon globally.
DON'T perform flamebait. Don't make a story just to bash something you don't like. That's basically begging for people to shout at you.