"Ich würde gerne" is softer and more polite than "ich möchte", which in turn is softer than "ich will". They all describe more or less the same emotional state. It doesn't make a difference whether it has been done before or not, so I'm afraid Alex is wrong in that respect. As a rule of thumb, when interacting with people, indirect expressions are considered more polite. Hence you use the conjunctive or you add "gerne" often for requests or when placing an order: "Ich hätte gerne ein Bier." "Ich würde da gerne durch, könnten Sie mich bitte vorbei lassen?" "Ich würde gerne mal dieses Kleidungsstück anprobieren". And so on.

Hey Belén, i came across this question myself in my studies a few days ago so I thought i'd share what I think about it. I'm not completely sure, but at the moment, i think the difference is that you use verb+gerne for things that you already have done and describe a preference for. I think gerne even means not just gladly but 'preferentially', literally. So, 'ich trinke gerne bier' would be for if you are a lover of beer, but 'ich möchte ein bier trinken' would be for placing an order, asking for it. With 'ich würde gerne' it might be saying what you would prefer in the future. What do you think? I'll ask one of my German friends.

"Ich möchte.." kann entweder mit Substantiven oder Verben benutzt werden. zum Beispiel: Ich möchte Wasser. oder Ich möchte essen. ***** "Ich würde gerne.." kann nur mit Verben benutzt werden. zum Beispiel: Ich würde gerne essen. Viel Glück!