Oh my golly gosh I have just had my two daughters birthday parties as they were both born in April just three weeks apart ( two years between them) and it was lovely to be able to create something magical for them. My 4 year old wanted a Dinosaur party theme and my 6 year old had a Beetles Bugs and Butterflies theme (rather than just butterflies as we wanted to invite boys as well). I could have combined them but each one has different friends and wanted different types of parties and I LOVE parties.
I think I'm in my element planning for one, once you get the theme going it can lead to all sorts of ideas. I wanted healthy food and less of the sweet stuff but I succumbed.
My tip is (sounds stupid ) but write every little detail down in advance and if you are buying things for party bags do it at least two weeks before so you will get it in time. Pass the parcel took me an hour to prepare ( with my 4 year old helping), she kept licking the sweets that were going in the layers so it took ages!