When you get past the initial cutscene you should talk to every character there is and collect everything you find on the ground. Also interact with everything in the room, don't forget the board.

The characters in question, that you need to find and talk to before Jerry, are:
the Super-Intendent, Stu the Park Ranger and the Hippy Girl (they will give you hints on where to look for Jerry). He's pretty easy to find but -- he's swimming in the lake found north to where the Hippy Girl is .

After you speak to him twice and read his mind, talk to the duck as well and cast the spell to be able to talk to him, hint: when following the spell, don't forget to add only one feather

Next you'll need to find Jerry's clothes, talk to everyone and also read their minds for hints. Couldn't find anything helpful? to the right of where the Hippy Girl is located there's a path, follow it and interact with the animal by the tree .

Now for the new quest, find food. It's not Jerry's old lunch . Hint: Talk to the Hippy Girl . After getting the food, return to the spot where the animal is, read its mind and cast the same spell as the duck but instead of a feather use two cat claws .

Talk to Cat and follow the new quest, hint: talk to the Hippy girl and if still don't know where to look for, talk to Ranger Stu . Return to Cat with the blanket and trade it for Jerry's overalls.

Return clothes to Jerry and watch the cutscene.

Find Romy, Romulus the cat, follow the paw prints and get past the now open gate and talk to the Ecologist, found through the first path seen when you enter the forest, also read her mind.

After finding Romy continue walking and interact with everything you find on the ground. Go left from the rocks and find the Hermit, talk to her and read her mind, then enter the building next to her and interact with the things inside. After that, continue walking to where you haven't been yet until you find a tree blocking the way, you'll need to cast a spell on it to get through it, it's the destroying one .

After getting through the tree interact with the animals, to get the next quest you'll need to cast a spell, hint: you only need to talk to Hedghog, cast the spell that makes you able to talk to animals and add two hedgehog spikes .Talk to them again.

To distract the Ranger you'll need to talk to everyone, hint: one of them will help you after you cast a spell, get to the Super-Intendent and talk to him, you'll need to cast the vanishing spell on the trophy . Now get to the waterfall, following the same path as when you found the animals and continue through, you'll need to cast a spell to talk to animals, adding the feather Romy gives you , interact with the animals again, then enjoy the cutscene.

First of all, you'll have to go to the waterfall and interact with the spilled potion, you'll get a new quest to recreate the potion, interact with Romy and everyone else, for those that says you shouldn't talk to, simply read their minds, don't forget to talk to Mother Duck , although they all say pretty similar stuff, the actual recipe for the potion is 5 of each mushrooms and one hibiscus flower , then you need to find who brew the potion, so talk to those who could be the witch. When you find out who it is, you'll get a new quest, find the prized possession (the coffee grinder), for that you'll need to talk to the people living in the forest, yes, even the animals .

final hint: read the Hermit's mind, the coffee grinder can be found inside the building next to the Hermit . After you return it to Winnie you'll get a new quest, locate casting site: for this you have to go to the waterfall and interact with the tree stump, then the other two, hint: one is near the Ecologist and the other one is near Mother Duck .

After interacting with the right tree stump a cutscene will happen. And that's the end of the game :]

[edit] Thank you all so much for the nice feedback! Your kindness is very much appreciated :]
[edit 2] Just corrected some grammar mistakes and added more space in between paragraphs to make it better looking. Thank you all for continuing to use this guide!