This should be short, yet contain the major result
Often this is the only part of your paper to be read (or scanned) by other astronomers

Simple in theory, but the order matters a great deal.
Typically the first Author has done the majority of the writing, and led the project
The second author also has helped significantly with the entire project
The third author etc. will have often played an important role in one or two aspects of the project
Make sure everyone's name is spelled correctly and all the usual middle initials are used.

This is the most important part of the paper.
No one reads a paper without first reading the abstract.
Often only the abstract is read...
It must be short (less than 250 words typically)
But it must also tell the reader:
    What was Done,
    What Hypothesis was being investigated
    What was in fact measured
    What Hypothesis (or model) was supported by your measurements
    Why this is important, and broader impact
This is the hardest part of a paper to write, and should be done last.
Use the AAS standard (see an example abstract here to see how this is done)

This section should tell the reader the history of what other papers in this field have discovered
for example,
       The age and distance to your cluster
       The mass, age, and evolutionary state of your variable star
       The nature of the extrasolar planet and star that you studied
Be sure and check NASA ADS for any papers similar to yours or
        on your object (do this before writing the paper!)
        Also be sure to check astroph as well.
One should try and cite the major papers that have led to the current understanding of the problem.
       Always cite the discovery papers...
The introduction should very clearly spell out what the problem is you are writing about, and why it is important.
Overly long introductions should be avoided, but complete understanding of past papers should be presented.
The last section in the Introduction outlines how your paper is written, section by section.

This is the easiest section of the paper to write (since you have done this)
Clearly spell out what was observed at the telescope. And for how long (total integration times).
Clearly note the telescope & instrument used. Cite the right paper for the instrument.
Summarize the instrument (size of CCD, size of FOV, etc.), note size of scope.
Use a table to summarize the list of targets that were observed, for how long, and in which filters etc.
Note any special techniques that you used to optimize your science (like windowing the CCD)
Note the weather conditions, UT date/times, moon phase, airmass, seeing, clouds, etc.
Note the calibrations (Darks, Flats sky and/or dome) that were also observed to help with the data reduction

This can be an easy section to write-up as well, if you have carried out the correct set observations & calibrations.
Tell the reader how you removed the signatures of the telescope & instrument.
Be clear in how calibrations were used etc. How did you make your "super flat"?
For example, you can say "the CCD frames were bias subtracted then divided by a super flat"
Tell the reader how you aligned the frames (imshift), how you combined all your frames (imcombine) etc.
Be sure to be clear about how more complex tasks (like Lucy deconvolution, or DAOPHOT) were used.
Clearly note how you used reference stars to normalize photometric timeseries etc.
Clearly present your reduced data in some (or all) of the following:
    In a table of photometry
    An final reduced image of your target
    A final spectrum (or time series)
Always include a discussion on the errors and error analysis of your observations
By the end of this section the "science" is ready to be extracted from your tables, and/or figures.

This section is where you actually "extract" that science from your reduced data.
For example,
    from your table of B & V photometry you can plot a Color-Magnitude diagram (with errors)
    Or from a timeseries you can create a power spectrum (with errors, and pick out significant periods)
    Or fit your planet transit data, smooth your data? and give errors.
Here one can use theoretical models to fit one's data and to derive difficult to measure quantities
There should be a careful discussion of errors (in particular systematic errors) here as well.

In this section one should try to relate how the quantities measured above relate to the scientific questions you are trying to answer.
Here you should be relating your work to the "big picture" presented in your introduction
How do these results compare to other similar studies? What is new here?
Why do your observations support one physical picture and not an other?
For example,
    From a Color-Magnitude diagram determine which  stars are members,
            and size, age, and distance to the cluster
    From the significant periods found from a star understand the interior structure of the star
            compare your results to other published ones
    From the best fits of the transit model determine the size of the planet in the system, and orbit
  

This section is optional, but it helps point out where you see the field moving
Note how your results could have been improved
Outline how much more could be gleaned from a better approach, or bigger scope etc.

This section should written just before the abstract
It should be longer and a bit more detailed than the abstract
It should restate what your goals were (briefly)
What observations you made (briefly)
What your main measurements were (with errorbars)
What physical model (hypothesis) is supported (and/or not supported) by your measurements
 

Here you thank all that helped make your paper possible
Thank the Steward TAC for allocating time at the 61inch for your project
Thank Betsy Green for helping/teaching you take your data .
Thank any funding sponsor (like NSF, NASA etc.)
Thank the telescope support staff if they helped you with a custom filter etc.
Thank external people that are not co-authors but did help you (like Prof Close in this case)

VERRY important to cite references throughout the text (otherwise plagiarism!)
Use the AAS standard (see example paper here to see how this is done)
Be complete as possible.
Be sure and check NASA ADS for any papers similar to yours or on your object (do this before writing the paper!)
Also be sure to check astroph as well.