How hasn't Happy Island Designer been posted yet ?! Haha
I'd advise taking it slow if you can, I understand the desire to have a perfect island but bare in mind that once that happens you'll be so far in the game you won't have as much left to do, so it's actually pretty good to not entirely be satisfied yet, that means you still have lots to explore and play with!
I unlocked terraforming a week ago now, and my island is almost there cliffs/rivers wise, otherwise it's a huge mess haha.
I agree with what have been said previously, I too focus on one small part and work on it until I'm happy with it (for however long that is...) then move on.
That said, the
Happy Island Designer Tool has helped me tremendously. It's much easier to envision what you want this way. You can also make several versions of your map to see what you like best, or rework small parts and save several options.
I also recommend looking at pictures to get some inspiration! It can really get the flow gowing if you're feeling stuck, just by realising what you like and don't like.
I can never stress this enough but don't forget that sometimes the best to do is to let go! Turn it off for a day, and come back when you feel like it, it does LOTS of good. ☺