One of the main reasons this board was created was to allow people a forum to get feedback on their ideas for lists, their writing, their selections, etc. FAQ and Review writers have somewhere to go to get feedback, so this board was created so Top 10 authors could, too.
Toward this end, this topic is a compendium of some of the suggestions the Top 10 List board has come up with over time. They span four topics: Choosing Your Topic, Selecting The Items, Writing the List, and After the List is Submitted.
Choosing a Topic
1. Brainstorm naturally. Don't sit down one day and say, "Ok, I want to write a Top 10 list. What should I write it about?" The best ideas are ones that come to you naturally, not ones that are forced out of your poor brain. If it's an interesting idea, it will likely spring forth from an unrelated activity, like actually playing a game or reading other lists. If you try to force it, you end up with crummy lists like the "Top 10 Video Game Horses" list I had wrote a couple years back, then had removed several months ago.
One of the activities that most often leads to new list ideas as well is actually writing a list. If you've already got an idea in mind that you're working on, be ready to write down new ideas as well. A lot of them won't go anywhere, but when you're in the writing mindset, you're naturally well-equipped to think of new ideas as well.
2. Choose a suitably narrow topic. There are two extremes when it comes to brainstorming a topic: there are lists for which hundreds of games would technically qualify for consideration, like "Top 10 RPGs", and there are lists for which you'd struggle to even think of ten games, like "Top 10 Interspecies Romantic Subplots." The best list topics are the ones that fall somewhere in the middle. You want a decent body of selections to choose from, and you want to have to at least defend your ideas a bit. At the same time, if the body to choose from is too large, your list becomes absolutely nothing but opinion.
For example, many of the early lists were topics like, "Top 10 SNES Games". Topics like that tend to be too broad, and as a result, reflect only the author's opinion. On the other hand, lists like one I recently proposed, "Top 10 Characters Named Cid", tend to be so narrow that you're basically choosing every possible item for the list. "Top 10" implies the best 10 out of a larger group; if there's not a larger group, it's probably not a great topic.
3. The search bar is your friend. There's nothing wrong with doing a topic that's been done before. However, searching previously done lists can provide valuable information. If the topic's been done a dozen times, maybe you'll want to put your own spin on it. Or perhaps you want to do something special to differentiate your list from a recent one. Reading a similar lists might also make you aware of things that you don't like about other lists in that general theme, so that you can then ensure you do something differently.
For example, two recent lists have focused on the crimes committed by game protagonists Mario and the playable Pokemon character. I thought a general RPG protagonists' crime list would be fun, but one thing that I didn't like about the other lists weren't specific about what 'crime' meant. To me, the crimes that should be listed were ones that humorously weren't discouraged within the game world, and thus, that became one of my formal criteria. And speaking of which...