Right now, I'm looking at some major over hauls of Fén. I think I've made a lot of mistakes and it might be in the interest of new conlangers seeking to make something from scratch [particularly Fantasy aimed] to hear me out and learn from my mistakes.
When I first started, it was a pretty amateurish thing that I intended to throw in the background for flavour. At that point I would have seen minor issues as something to potentially offer a quick fix around, but putting my conlang on a proper wiki has motivated me to try and over come a lot of these issues and make a consistant language which people could actually talk with. Considering I actually had/have a relatively well developed language save for a few rather deep difficulties or exceptions here and there, a lot of the lessons are not only hard learned but something where I have had to gain a good understanding of why these things don't work.
I originally based the Phonology off of Irish because it was rather unique and I enjoyed it. At the time, I had minimal understanding of the IPA and details/reasoning behind the grammatical sound changes in the language. As a result, lentition was either borrowed from Irish or else unnatural and arbitrary. I found myself simplifying things and removing the sounds I didn't use, which I now regret. If you are building a natlang from scratch, I'd recommend looking at the IPA chart itself, picking sounds you are comfortable with and then looking at how sound shifts over time. Maybe pick up a sound or two you are not familiar with. If you intend to do anything more than put it up here or write in the background of stuff, then phonology is the first thing people are going to pick up on. Right now my language sounds "Irish" and it's going to be relatively hard to balance that out. I'm thinking of just throwing in French influence and nazalization to try and alter things, but most possibility feel forced at this point.
Unique Morphemes. I'd recommend hitting up a short list of Indo-European words if you can find it. Ideally one written by authors more on the skeptical side of things to keep it relatively short. These are the words that don't change over time drastically and a lot can be made from them. I made the mistake of inventing only a handful of words from scratch and now find myself having to do a rather radical pour over because some compounds simply don't make sense; Hand and other really basic words shouldn't be formed from compounds of more complicated concepts.
Finally be careful with Grammar. I made Fén an isolating language for the sake of simplicity and now find myself pouring over it for a way to explain the grammar. In itself, I feel the matter is rather simple but my lack of grammatical terms and going forward without a solid understanding of concepts has left it rather messy at best. At its heart, Fén is just a language that loves clauses. It probably takes after my unfortunate affection for run-on sentances, but now I find my ability to convey what I need to rather lacking in a language where word order is everything.
So if you're remotely interested in Fén, espect some radical changes soon, mostly regarding the above. More over, if you think you can help me out with it, I'd love to hear from you.