Keeping your tree golden as you progress, or reguilding a tree
Here's a simple recipe for keeping one's tree golden as one learns a language. It can also be used with a decayed tree, or at any point.
First, select how many lessons you want to do each day. This is the minimum.
Second, use Duolingo every day, or as often as possible.
Third, when you start, do you have any non-golden skills? If you do, practice those. You can start from the top, the bottom, or by any other rule or arbitrarily.
Fourth, if the tree if golden and you still have more than one lesson left, do general strengthens until you only have one lesson left.
Fifth, when you have only one lesson left for the day, if your tree is not golden, practice a non-golden skill. If the tree is golden, progress with a new skill.
Sixth, if you want to do more practice than the required, do general strengthens.
This works because there is lots of repetition, so you will learn the lessons and make only few mistakes. Don't use hints unless you need to. This will, the words will decay only slowly, and the tree will tend to remain golden.
If you are in more of a hurry and want to progress, than here is a variant:
First, decide how many lessons you want to do each day.
Second, when you start, first do a new lesson if you have not yet completed the entire tree.
Third, if you have lessons remaining, practice non-golden skills. Do it in any order you want.
Fourth, if you have lessons remaining but the tree is golden, do general strengthens.
Fifth, if you want to practice more, do general strengthens.
This might not lead to a golden tree immediately, but it will over time at least after you have completed the entire tree. But you wanted to hurry, right? That's the price you pay for hurrying.
I'd actually advice to do skill specific rather than general strengthening exercises. I'd also advice to keep all skills at around the same strength (for example 3/5, 4/5 or all close to golden but not just yet) rather than focusing on grinding them to gold one by one.