MacBook Pro used in smoking area
To start, you'll want to power off your MacBook Pro, and clean it thoroughly (but carefully) with a microfiber towel. If you do this dry, you run the risk of abrasion and scratches, but you also don't want to soak your MacBook Pro with any liquid. 

External Cleaning
Use an electronics screen cleaning liquid, preferably one with an "Apple Approved" label. Don't use anything alcohol-based or otherwise corrosive externally, as it will damage the rubber and plastic parts. Spray the cleaner directly on the microfiber towel, not your MacBook Pro. 

Most Apple approved screen cleaning liquids leave a thin film you allow to dry, then gently polish away, not unlike wax on a car. Avoid open ports, thoroughly but gently clean the keyboard, hinge area, and speakers. These areas tend to accumulate a lot of gunk. 

Internal Cleaning
Here's a step-by-step tear-down of the 2013 MacBook Pro. 

https://www.ifixit.com/Teardown/MacBook+Pro+13-Inch+Retina+Display+Late+2013+Teardown/18695

In addition to their required tools, you will need:
• Electronics Cleaning Liquid, usually sold as "Screen Cleaning Liquid"
• Microfiber Screen Cleaning Cloths
• Electronics Cleaning Swabs (lint free Q-tips) optional
• Paper Towels
• 70% or (ideally) 90% Isopropyl Alcohol 
• Medium bristle toothbrush or paintbrush (optional)

You may want to invest in an anti-static wristband: They're inexpensive, and will save sensitive electronic parts. If you do not have one, disassemble your MacBook on a wood or metal surface, protected by a static-free towel: Microfiber works well, but only the "smooth" type, not the terrycloth type.

In Step 12 of the tear-down, you will see the fans being removed. This is optional: A good cleaning with canned air will most likely rid you of the problem. Take care not to blow the fans around too much. You won't clean them this way, and it may be bad for the motors. As an "extreme cleaning" option, replacing the fans will also get rid of the smell.

Take special care in wiping out the aluminum bottom case door -- The bare aluminum door, not the electronics -- with an electronics cleaner and a microfiber cloth or paper towel. Dirt, dust and debris tends to accumulate there. 

You can gently clean the circuit boards in your MBP with 70% or 90% Alcohol (do not use Rubbing Alcohol with high water content), but this will depend on your comfort level working with electronics. Avoid the battery while doing this. Isopropyl evaporates quickly, and is used for liquid damage remediation for this reason. I have used it to thoroughly clean my 2009 MacBook Pro several times, and am typing on it right now. 

Be careful and gentle with the electronics, and clean it well. Good luck!