I think a common newbie mistake is handle waaaaay too long. Fades waaaay too long.
Newbies are firghtened of too sharp a fade and all the books say blend it it in gently.
The problem is you end up with the centre third stiff, and then the two ends whip tillered. giving what I call a 'square' tiller 'cos it looks like |_| but up the other way.
Have a trawl through my bowyers diary, there are plenty of pics of bows being tillered at various stages. , but and also some vids.
A good trick is to hold a plate, mug, CD or whatever up in front of you as you look at the bow, it will show where the bend isn't smooth.
I've got an Elm warbow in the early stages on my blog there at the mo', you can see it's not perfect, if you hold up a Cd to the pics you can see where it is stif and where it bends too much... I also explain how I'm going to fix it.
http://bowyersdiary.blogspot.co.uk/2013/10/busy-weekend.htmlDel