Objectives:
(1) To name your topic title shorter
(2) To better express your ideas and catch more attention of readers

Notes:

The guide only help writers to construct their ideas, sentence; choose good keywords, hooks, etc. and make their topics, or posts look more attractive at a blink of eyes.
It does not change general quality of topics/ posts.
Determinant things are creative ideas, and details, examples to support/ expand/ explain core ideas.

Sources:

Avoid
Tags within brackets or abbreviations

Quote from: theymos on August 24, 2012, 07:31:55 AM

Some people like to put "tags" in the title within brackets. Like "[GLBSE] [ANNOUNCE] ASDF: Generic asset". I personally don't like this style. I prefer to include the tag info within the sentence, like "Announcing ASDF, a generic asset on GLBSE". When tags are really necessary, it may indicate that a new subforum should be created.

Newspaper capitalization

Quote from: theymos on August 24, 2012, 07:31:55 AM

Use normal capitalization, not "newspaper capitalization". "Thread title style guide" instead of "Thread Title Style Guide". Capitalize the first letter of the title unless it a trademark like "eMachines".

Timepoints

Quote from: theymos on August 24, 2012, 07:31:55 AM

If the title is composed of only one sentence, don't include a period at the end. If it contains two or more sentences, put a period after each sentence, including the last. Questions must end with a question mark.

Unnecessary hedging
Don't overuse hedges, because your sentence will become more difficult to understand

Remote verb
Keep your key words and verb stay as closely as possible because remote verbs will blurr what you want to say.
"Merit system, after its about 2 years history, and few adjustments, has reduced spam"
This one is better:
"Merit system reduces spam, after two years"

Respectively
In case you present a long list of things (>= 4), with figures, you should avoid using respectively, because readers will have to backwards read objects you mention and compare with figures you present. It certainly cost readers lots of time and give them a bit uncomfortable feelings.
Personally, if I present data with four objects and above, I will avoid using respectively.
Example: (Figures used in this example are not real data)

There are three boards that have most non-sense posts, gambling discussion, altcoin discusssion, trading discussion, and bitcoin discussion with total non-sense posts per day at 10000, 20000, 25000, and 30000 respectively. ⁽¹⁾

There are three boards that have most non-sense posts, gambling discussion (with total non-sense posts per day at 10000), altcoin discusssion (20000), trading discussion (25000), and bitcoin discussion (30000). ⁽²⁾

The (2) style looks better.

Should
Key words/ hooks

To catch attention of readers
Should be put at the beginning of title.
Key words immediately disclose what you want to bring to readers

"Users were affected to rank up"
There are so many reasons, so if you want to point out exactly merit system as a cause, you should use this title
"Merit system affects rank-up speed of users"
I use two keywords: merit system, and rank-up speed (to emphasize that the effect is on rank-up speed, not de-rank speed).

Active is better than passive sentence
"Merit system affects rank-up speed of users"
"Rank-up speed of users was affected by merit system"
I do believe the first one is better

Questions: question mark and question words (what, why, when, how)

Only use question mark if you ask for something
Use declarative title to say what you found, rather than question mark (?)

"Does merit system affect rank-up speed of users?"
With this one, readers don't know what you will present in your thread. They will easily think that you ask for reasons, rather than present your findings and things that you think are reasons.

Condensation of your title

Keep it as short as possible (to save reading time of readers, catch more attention, and to satisfy character limitations)
Omit all needless, superfluous words (includes useless adjectives): they obscure meanings and distract readers to main points
If your thread title is not interesting, not attractive (lack of keywords, hooks, too long), they will ignore your thread

"Merit system over its two year history possibly affects the general rank-up speed of users"
This one is too long. If I am reader, I will ignore it.

Use declarative rather than a neutral title
Let's compare two titles
"Influence of merit system on forum users" (Neutral)
"Merit system reduces spam, restrict spammers to rank up" (Declarative)
The second one is much better, because it directly emphasizes which sort of influence of merit system writer will discuss.

Tense
Using simple present or simple past

You can apply those things for your posts, to make your topic sentence more attractive, and more informative. I usually ignore posts that written without topic sentence.
There are more important things to make your posts not only attractive at first glance, but also informative and have above-average quality
Bitcointalk posting etiquette