I'm not sure how long you want your scripts to be, but feature length films are about 120 pages. 1 page is about 1 minute of the film. Now, not to sound harsh or rude, but what makes you think a script this long is going to go from your head, to your fingers, to the computer keyboard in an instant? It takes even the pros months, if not years, to complete a script. Creativity can't be forced; it just can't. So don't beat yourself up over how long it takes. There is no set time that it should take to write a script. If it takes 10 years, then it takes 10 years.
Now with that being said, also realize that comedy is probably the hardest content to write. You have to be able to distinguish the difference between what you personally find funny and what actually is funny. Unfortunately, I have no experience writing comedy, so I don't have tips for that, but I can tell you that I day dream a lot and think of some pretty funny stuff. Maybe that's all you have to do. Always carry a little tablet and pen around and just jot down ideas that come to your head when you least expect them. If you don't write them down, you will never remember what your idea was when you find time later to write it down, and thats the worst.
I took a script writing class, and could go on and on giving you tips. But to make things easy on me I'm going to suggest you buy the book I had to buy for class. It's cheap as hell. It was about 12 dollars at Borders or something. It's written by Syd Fields and it's call The Screenwriter's Workbook. It's not really a workbook, but it kind of is in a way. It guides you through the script writing process as you write your script. I've been told that anyone who is any good at writing scripts knows about Syd Fields. Apparently he's the guru of script writing. So trust me, this may be the best 12 dollar you spend if you are serious about script writing.
Also remember that when you're done with your script, no matter how amazing it is, there is always room for improvement. So when you finish your first draft, go over it and make changes where you think the script can be better. And then when you're done with that, do it a third time. And a fourth until you are completely satisfied, and I mean really satisfied. Don't just be satisfied because you're sick of looking at it. I forget who told me this or where I read it (maybe it was in the book I suggested), but I remember a saying that was something like,"Even if you don't want to write today, just write anyway. You might not write as much as other days, but you're writing won't be worse than other days." It was something like that. The point is, just keep going.
Good luck. And believe me, you want this book. Just get it. I don't care if you're broke or what. I guarantee you won't regret buying it. It's an easy book to read too. A 3rd grader could read it. I can't stress enough how valuable this book is if you are serious about script writing. Just get the book. The Screenwriter's Workbook by Syd Fields.
