Extreme Gardening is a fun game if you want to kill some time, and a frustrating game if you're going after medals. The gameplay mechanics are that you have 3 seconds to memorize what the tree should look like, and then 10 seconds in unresponsive and clunky mouse controls to make it happen.
1) When you run into a level you have difficulty with (i.e. 12, 13, 14) take screenshots of what they're supposed to look like, and have the screenshot sitting next to the game as you play. This will save you from having to remember every minute detail, as they will all be there on the screen for you. Even better, tape a piece of translucent paper over the screen and trace the shape you're supposed to make, and then just clear where appropriate. Taping paper is the only somewhat reliable way to get all golds; screenshots will only get you to silver.
2) If you're chasing all gold medals without a piece of paper, stab yourself in the eye, because you're more likely to get satisfaction from blinding yourself than you are from chasing 15 gold medals in this game in that way. If you want to get all gold medals without committing suicide, you need to use paper.
3) To save time, which is vital, rather than waiting for the game to tell you to go, you should already be holding down the mousebutton. The game doesn't check when you push it, only that you push it, so if you're already holding it down you'll be able to take your reflexes further away from being a deciding factor in your score.
1st Bronze (5) - Your very first bronze! Eke out a level.
1st Silver (10) - Your very first silver! Get halfway between the bare minimum to pass and 100%. So if you need 80%, 90% will get you the medal.
1st Gold (10) - Your very first gold! Get 100% on a level. Most likely to happen on levels 1 and 15.
Day Area (10) - Complete day area! Finish the first 5 levels.
Sunset Area (25) - Complete sunset area! Finish levels 6-10.
Night Area (50) - Complete night area! Finish levels 11-15.
All Bronzes (50) - Collect all bronzes! Finish all levels with bronze or above.
All Silvers (100) - Collect all silvers! Finish all levels with silver or above.
All Golds (100) - Collect all golds! Finish all levels with gold. If you want this medal, you're going to be taping paper to your screen so you can trace things. As far as we are aware, the minimum scores for gold medals on each level are as follows:
level 1 "Introduction": 100%
level 2 "Basics": 99%
level 3 "Hoop": 100%
level 4 "Treesome": 100%
level 5 "Horticulture": 99%
level 6 "Nouvelle Vague": 99%
level 7 "The Man": 99%
level 8 "What?": 100%
level 9 "Connection": 99%
level 10 "Perfection": 100%
level 11 "Grrrrrr": 96%
level 12 "Forest": 99%
level 13 "A Classic": 95%
level 14 "Masterpiece": 91%
level 15 "Future Art": 100%