Before you paint your foreground, try to add some additional detail. You can add them after the foreground is created but it is easier to think ahead.
When you initially add a tree trunk it can look rather simple. But then it will become more impressive as you continue.
As you add in leaves consider the shape of the tree you are painting and think about putting in dark leaves before adding in lighter ones.
You final stages could go on for quite some time. I find that I return to paintings days later and continue to add small touches until I am happy with it. I hope you enjoy painting and that this has been helpful for you.