KISS is an acronym for "Keep it stupid simple". The KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore simplicity should be a key goal in design and unnecessary complexity should be avoided.
If it is complicated it is wrong.
No grand solution or invention of mankind began complex. It started simple and evolved gradually. Humanity took 10,000 years to be where we are. The cars were horses, then Ford-T and now are Ferraris. The same for the software.
Produces small code continuously.
Do not try to create a big and complex code. If you are going to this path then stop! You are developing wrong. According to agile principles you have deliver working solutions which meet the goals of all stakeholders. Is better continuously deliver small slices that work than spending several weeks or months and not deliver what the user need.
Short codes are manageable.
A short code is manageable, understandable, testable and a lot of things. Try to keep it simple and short. It is easier to think. Keep it in mind.