Below is a list of the steps I usually follow in processing deep sky images. As new techniques are developed I vary my approach, but I'll try to keep a set of lists that reflect how I've been processing my images over time.

Standard Processing Workflow by Workspace in PixInsight 1.8.9:

1. Processing

Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and manually reject a few frames
Weighting, registration and integration with WBPP
RGB Combination for RGB frames
Dynamic Background Extraction on luminance/narrowband and RGB images
ImageSolve RGB, then run Spectrophotometric Color Calibration, using Average Spiral Galaxy white reference
BlurXterminator using Correct Only on luminance/narrowband and RGB
BlurXterminator on luminance/narrowband and RGB
NoiseXterminator on luminance/narrowband and RGB
DynamicCrop on RGB and luminance/narrowband
For planetary nebulae and some other images, create inverted narrowband images: Crop, Invert with Ctrl-I, Apply STF to Histo Trans, and Save

2. Luminance/Narrowband Stretching

Histo Trans x 3
Curves Trans
Mild Localized Histogram Equalization to enhance internal contrast (if desired)
TGVDenoise (if needed)
Final Curves Trans
Aggressive MultiscaleMedianTransform to smooth background lumpiness (if needed), using an inverted luminance mask to protect brighter areas
For narrowband images, StarXterminator to create starless images

3. RGB Stretching

Create a saturation mask: apply ScreenTransferFunction to Histo Trans, then apply to the stretched luminance/narrowband image(s). Enlarge the mask with MorphologicalTransformation if needed. Blur the mask slightly with Convolution.
Histo Trans x 2
Curves Trans to boost saturation, using the saturation mask to prevent spurious background colors from being boosted
Curves Trans to brighten
TGVDenoise, if needed
Create an RGB stars-only image with StarXterminator

4. Color Blending

[For LRRB images: LRGB Combine (using Ha as lum for HaRGB images)]
[For tricolor narroband images: PixelMath to blend narrowband images, mapping SII:Ha:OIII to R:G:B or Ha:OIII:OIII to R:G:B, or one of the Dynamic Narrowband blends]
[For OIII-rich PNs: Curves Trans to shift nebula toward blue in narrowband image (pulling down green and pulling up blue, while keeping the LRGB balanced)]
[For Ha-rich PNs: Colorize to red with Curves Trans, pulling up red and pulling down blue and green. [Usually] Use this as a color layer, blending it with Ha as luminance in an HaRGB combine]
[if desired: StarXTerminator to create starless and stars-only (star mask) images]

5. Background Subtraction (Artificial Flat)

For LRGB and HaRGB images made with a moving-mirror SCT: Broadband images captured with my (non-Edge) C11 usually had circular artifacts left over from flat calibration, because it’s basically impossible to create accurate flats when the mirror shifted while capturing light frames. To remove these artifacts, I create and subtract an artificial flat, which is simply an image of the messy background, with all stars and imaging targets removed.
a. Create an image of the background by removing stars with StarXterminator
b. Clean this image up in Photoshop, removing the target(s) and any leftover stars
c. Blur this background image slightly (otherwise in the next step you’ll remove all the noise, creating an unnatural-looking noiseless image)
d. Back in PI use PixelMath to subtract the background image from the main image (adding a pedestal, to avoiding having a pure black background).

6. Add Stars (for narrowband images where stars were removed)

PixelMath to blend RGB stars-only image and colorized narrowband image using the formula ((1-$T)*(stars_only))+$T, where $T is the colorized narrowband image
[For planetary nebulae: In Photoshop, layer this new image onto the RGB image using a mask. The RGB starfield usually looks better than a starfield made from the narrowband images, so this method uses the nebula-plus-stars image only where the PN is.]

7. Final

Final Histogram Transformation
ICC Profile Transform to sRGB
Rescale as desired
ImageSolve
Create annotated images with the AnnotateImage script, using some custom databases to extract quasar redshifts and galaxy clusters
Save final image, annotated image, and inverted narrowband images (if any) as JPG