That's the entire idea of Ikea. That's how the shop makes its fortune. Why else would they design the layout so that you HAVE to walk through the entire shop rather than being able to go directly to the section you want.
The only tip here, if making a list doesn't work, is to buy what you want from a different shop when at all possible or ask someone else to go on your behalf!!!
I find it wears off - we were always there when we moved to our new house and I kepy buying (very weird) stuff, but after a while I would look at stuff and think, no, I don't really want that in my house. It's a bit like Facebook - totally addictive for a while and then you think, ah well, it's a bit sh*t really, innit?
I once went round with my dp and as we were approaching the checkout with our TWO trolleys piled high, having spent the best part of two hours there, we suddently had a tot up of what it was likely to cost and then with the thought of the queues ahead just said, 'shall we do a runner?'.
We left the shopping trolleys there and then and get the hell out. very inconsiderate in a way but we realised how easily we had been duped into filling up with all sorts of plastic milarkey, wild patterned textiles and various object d'art (if you could seriously call them that!). We lvied to fight another day.
I wish I could say that was the last time I went there, but now I am a lot more discriminate about twhat I pick up.