Question: When asking an "ID My Bike" question what information about the bike should I include? 

Would a good "ID My Bike" question need all of the following or are there a few key things that would offer the best chance of an ID? Maybe something like - if these three things are included the chance of ID is 50/50. If these two things are added to that the chance goes up to 80%

**Pictures** (maybe some coaching on how to take good pictures) 

* every major frame joint
* all decals/logos/stamped names
* every component
* Other

**Words**

* Serial number
* Information about my current knowledge of the bike
* Links to information I have found so far
* Other

Answer: 
First, accept that the chances of your bike manufacturer, brand or model being identified are low, effectively zero in many cases (repainted BMX frames, generic 80's drop bar ten-speeds, 90's inexpensive hybrids ...)

Having seen a great many id-my-bike questions on this site I think the goal is not so much getting the bike identified but avoiding looking like an idiot, collecting sarcastic comments and getting your question closed as a duplicate of [Why shouldn't I care what model/make/year my bicycle is?](https://bicycles.stackexchange.com/questions/52060/why-shouldnt-i-care-what-model-make-year-my-bicycle-is) within 20 minutes. 

That said ...

An absolute necessity is well lit, high resolution, straight-on photo of the whole bike, right way up, from the drive side, with an uncluttered background.

Include the year of sale when new if you know it (or a guess). 

Description or photos of major groupset components helps. Knowing the series/level of derailleurs, crank, shifters, wheels etc. can help narrow down the year range and model level.

Any other info or photos you can provide won't hurt, but don't raise the probability of an identification much it seems.

A piece of info that is generally left out that I think might help in some cases is the country or location where the bike is.

Including the serial number generally won't help. Collectors have made databases of numbers of a few collectable brands, and sometimes someone will be able to decode a numbering scheme, but in general they are meaningless as manufacturers don't provide a serial number lookup that will provide model or component configuration to the public.
This answer emphasizes a few things in other answers for clarity. In general, we ask for clear photographs of the entire bike, and preferably some close ups of select parts as well. Be aware that these are usually necessary *but not sufficient* to ID a manufacturer, model, and year. Identifying a manufacturer is easier, identifying model and year is harder.

Bicycle companies typically rely on decals, usually on the down tube at minimum, and head tube badges for branding. If you have those in the photo, you usually know who the bicycle *manufacturer* is. Of course, if those items are present, then the OP usually has the information to identify the manufacturer already. Nevertheless, not all head badges state the manufacturer clearly, but they can be recognized by enthusiasts. One example is Giant Bicycles' head tube badge. Naturally, some bicycles have had their decals and/or head badges removed.

Failing that, with steel bikes, the design of the frame lugs and fork crown lugs can sometimes be informative, although not all frames use lugged construction. Some other design elements on bikes in general can be distinctive, which is why Criggie mentioned things like unusual-looking dropouts, sometimes the seat cluster. As another example, some Colnago steel bicycles (e.g. Master and Master X-Lite) used star-shaped down tubes on the argument that they had higher torsional rigidity, and I don't believe anyone else used these. I think that these unusual design elements are more rare, however.

Identifying the *model* and manufacturing *year* of the bicycle can be harder. Sometimes, enthusiasts can match a paint scheme to a catalog, thus providing model and year - if someone posted a scanned catalog online, or if they collect catalogs, or if there's an example of the bike online, e.g. on Bicycle Blue Book (but that tends to cover more modern bikes). We can make guesses if we recognize the components or other frame features. For example, in the first photo Criggie posted, the components look like 9-speed Shimano 105, which was current in the early 2000s. The bike has a quill stem, rather than a threadless headset and stem, and these were less common on early 2000s bikes. So, it's possible the bike is from around the early 2000s, but it's also possible the components were refitted and the bike was from the 1990s.

It's been stated elsewhere, but the serial number is usually not helpful at all. Presenting the serial number alone is worthless, and it is quite possible that the question will get downvoted and maybe closed.