But fear not! If you follow this advice, you can be amassing tags like nobody's business.
5 Habits of Highly Effective Testrunners
1. Include multiple prompts.
This is pretty common knowledge at this point, but it is very important! A testrun post that's just a single post is going to be hit or miss by nature - including mutliple prompts is a good way to give anyone something they're interested in responding to, no matter what kind of RPing they like to do. Three is a good magic number - four is fine, but five or more will start to dilute the pool and people might end up ignoring most of them.
Make sure they're plenty different prompts, too! Don't just do three battle prompts; at that point you might as well have just put up one prompt. Think up three different situations that might come up in RP - a fight scene, a date scene, and a serious dramatic conversation, for example.
2. Keep in mind the game you're apping for.
Do your research! Make your prompts look like they really are from the game you're looking at. If you need inspiration, look at what other people have posted about in the game itself recently. Look up their backlog and reference a past event.
This also applies to the technical side! Make sure the format of your post lines up with the format the game prefers. Don't do a journal-style testrun entry for an all-prose game.
3. Have dialogue in your prompts.
To get people to be interested in your post, you need to give them a good idea of what the character is like. This requires talking. If your tags are all silent action, it makes the resulting post look somewhat generic, and hard to appreciate what makes the character unique and interesting. The simple addition of a little dialogue can turn a bland scene into a prompt overflowing with tags.
If your character is actually mute, you'll have to make an exception, but even for very quiet characters, try to have at least one prompt with a little talking in it. More, if possible.
4. Have action in your prompts, too.
The above being said, a testrun post absolutely cannot stand on dialogue alone. Remember, you have to set the entire background for the scene in each prompt, as you don't have established CR to play off of. Either have some narration to set the scene, or just an explanation of what kind of background built up to that scene happening. It really helps people get into the swing of your post, and thusly makes responding easier!
5. Consider the other person.
This is the most important one, the golden rule. The true measure of the quality of a testrun is not the prompt itself, but the threads that follow. So, ask yourself: If I was responding to this post, would the resulting thread be interesting?
Always plan the post from the angle of what kind of threads will come out of the prompts. Remember, you're making this for other people to reply to! Prompts that give other people opportunities to be interesting or entertaining are a plus. Prompts that show off how your character is cool without giving other people much of anything to say in response are a minus. Prompts that people can respond to in multiple ways are huge bonus points. Doing a fight prompt? Spice it up by allowing the responder to be the enemy, an ally, or an enemy hostage.
For dialogue-heavy prompts, don't just make it a monologue; make it the start of a conversation. Kick the dialogue off with a clear interest (or at least willingness) from your character in having a conversation. It also helps to establish a clear topic of conversation, to ensure that it doesn't degrade into vague small talk.
Most importantly, be creative, fun, and entertaining, and the people will flock to you for fun and RP. Happy testrunning!
If you have any further questions about testrunning, comment here and I'll answer as best I am able.