Review the Part 61 Aeronautical Experience requirements for private, IFR, and commercial. Confirm you meet them. Identify any gaps.
Find an instructor who has had several people pass the commercial practical test. Pay him/her for an hour of ground time to review the requirements above and your log book then develop a training plan to get you ready for three check rides. Your plan can include things such as flying to/from the local practice area under the hood and flying an approach after maneuvers.
You need to take three written tests. You can study for all three for very little additional effort over studying for one.
Do all of the training in whatever "complex" aircraft you will use for the commercial check ride. This way you accumulate whatever hours the FBO/insurance require and gain familiarity while training to proficiency rather than adding on those hours later.
You have to learn the maneuvers that are required for the FAA Commercial Certificate which you probably have not done before, but most of what you have as experience will still be useful.
If the Commercial Certificate is your goal, plan that from the beginning; don't do each of the three items in isolation from a bigger picture.
Good luck!