Sorry for my english, I'm ukranian.
1 - Behave like professional. If you are making games for big stores, like Steam (I have tutorial about that, go check it out), you should do it professionaly. Sharp corner or bug? Character behaves strangely? Game is foolish? DESTROY! Make your games like you make cookies for your mother - with love. Attention! Your game is not edible. If even game looks foolish, make it a style.
2 - You can do that! You write your menu plan with awesome GFX, but open Construct and think: "nope, Construct is not able of doing that". Rethink it. Construct does not make games, YOU make them. I am real programmer, and I have seen how impossible ideas came true. Another thing: you need to fight your lazyness.
Now, from theory to facts.
3 - don't miss 'System' expressions:
There are loads of awesome math, random, complex and other formulas that can help. Never miss them.
4 - Sort everything. If something in your project is lost - it can be realy big problem.
ALWAYS USE: object folders, event groups, variable groups - these can save your project. Always name them properly. And always name variables properly.
5 - Use 'Function' object to easen you life.
6 - Be creative. Do not use other's creations. Use custom fonts: Construct supports any TrueType Fonts. (.ttf) Use only your own music.
7 - From the beginning of project try to make ALL control types avaliable.
8 - Psst!.. You can also make programms, websites, videos and lots of other stuff using Construct!..
9 - Enjoy creating with your friends - animators, musicians, scripwriters.
10 - The last one - practice, practice, practice. You will not make good game, if you are not experienced.
Sorry for shortness.
"The truth will always be hidden, unless you create truth" - whoever it was (me)