The following will help you in preparing and actually cleaning the sofa.

Vacuum the sofa, its pillows and its cushions with the hose attachments. Do not forget the arm rests and backing of the couch. This will clean loose dust and dirt.

Dust the wood areas with a soft rag and a cotton swab for the area between the material and wood.

Find your warranty. If it is still in effect, the warranty may be null and void if you apply any cleaning solutions. Call the company for cleaning instructions.

Determine the sofa's fabric. This tag is typically found under the cushion area.

Buy shampoo specifically for your sofa's fabric.

SRent a rug shampooer.

Cleaning
Assemble the shampooer according to its directions.

Test a small area of the sofa. The best place may be the back of the couch or under the couch if possible.

Clean the entire couch. This will prevent watermarks.

Allow it and all its parts to dry before reassembling the cushions and pillows.

Tips & Warnings
You may want to try a carpet foam cleaner for spots that are still present after the cleaning. Again, TEST an area prior to applying.Some instructions will say dry clean only. You may want to use a steam cleaner on that couch.

Again, TEST it first.Cotton and wool fabrics may shrink. It may be wise not to shampoo the sofa but to spot clean it.