Read about families, containers, functions, global layers, arrays, dictionaries, timelines etc. Knowing how to use these features will save you many days/weeks of needless work.
Create families early! If you are adding your first enemy, create Enemies family straight away and add behaviors and instance variables only to the family. Upgrading a bunch of objects to a family later on will be a difficult and boring task.
Name your objects properly and organize them in folders.
Comment your code.
Avoid using hard-coded values and "magic numbers".
Back up your work at least once a day.
And finally, check out this post with great tips from Fib:
construct.net/en/forum/construct-3/how-do-i-8/order-thinks-develop-game-153820