Rongnongno Loc: FL

First recommendation is to calibrate both the monitor and the printer. I strongly suggest that you send test images to your printer (outfit if not local).
The second is to get the printer ICC for the paper selected.
Note that you must set the color space as required.

This is all good but far from enough.

Note that you will need to do this for each size you use and save an exported version for each, according to your printing outfit requirement.

Now, past this introduction...
A) Crop the image using the ratio you will need.
 - Use this to straighten the image at the same time.
 - Remember to leave a margin for possible framing. Also, you might want to adjust the canvas after selecting the ratio.
B) Resize the image (Alt-Ctrl-I)
 - Check if there is a preset that correspond to what you need. If so, select it and proceed to step (C)
 - Adjust the DPI according to the printer requirement
- Change the width drop down to inches or centimeters
 - Enter the dimension you need
 - Save as preset if you know you will need this again
C) Re-sampling an image will influence the color and sharpness
 - Verify that the colors do not need to be adjusted (contrast, luminosity)
 - Sharpen the image, the method is up to you.
D) Export the result to the format required by your printer.
E) Repeat for each size you need. There is no shortcut here.

Note: This is a draft that needs commenting.

dpullum Loc: Tampa Florida

" Remember to leave a margin for possible framing. Also, you might want to adjust the canvas after selecting the ratio." Good point, I am into using 1/4 flooring laminate to do gallery wrap and mirrored edges if an additional complication.

As usual Rongnongno gives good advice.

Monitor Brightness and Room Lighting ... Black Boxing [3 sided shielding with black foam board] the Monitor is useful to eliminate influence of room light is useful. Some have monitor brightness linked to the sunrise/sunset [I do]. Remember... Monitor is radiation vs print which is reflected from the room lighting... Will the printed photo be viewed in candle light 1900K or outside on a cloudy day 10,000K? Light is indeed a sticky-wicket. I use photos from the internet designed to calibrate brightness and color. Right or wrong the monitor should be close to the print. If both wrong and you like the look on the monitor and the print looks the same.... hey... fine. Do two wrongs make a right?? humm
http://www.3drender.com/glossary/colortemp.htm

I calibrate using photos google and take your pick example: http://tomyeah.com/images/Monitor%20calibration%20chart.jpg