InDesign Workshop

Images:

Resolution= 300ppi
Actual Size
Colour mode: CMYK or Greyscale
File format= .tif or .psd

Open the image with Photoshop if it is a jpeg to start with...
Change the resolution to 300- if you do need to change it, untick 'resample'

Image > Mode > CMYK
Save the image as TIFF or Photoshop file.

Open the InDesign file again > Rectangle Frame Tool (this allows you to place your image into the exact area you want)
Filling a frame with the image: Object > Fitting > Fill Frame Proportionally

Click on the 'Links' palette, select each image and look at the 'link info' just to confirm all the settings are right.
IF you need to edit the image size again, right click the frame with it in and open with Photoshop. Change the percentage in Photoshop to the same percentage that it is in InDesign. The image will automatically update in Indesign.

Booklet:

File > New Document > Print...choose the size you want if its one of them.
-Have to work in a multiple of 4 pages
-Keep Facing Pages ticked
-Margins > bleed and slug > 3mm for all

Saddle stitch book binding:

-First and last page is a single page not a spread.

How the pages would be printed for a 16 page booklet for example:

L                  R
16                1
2                  15
14                3
4                  13
12                5
6                  11
10                7
8                  9

When printing:

• Print booklet
• Booklet type: 2-up saddle stitch
• Print settings
• General > choose the correct printer > tick print blank pages 
• Setup > Paper size (ONLY if bigger than A4, select A3, A5 would stay A4) > Orientation: the second option 
• Marks and bleeds > tick crop marks
• Click printer > Show details > Two sided: short edge binding (always for a saddle stitch)
• Print 
• Preview, check it is all how its meant to be