How long to lead train ?

just wondering what your thoughts are, as from tomorrow i can walk Tobie.
Ive had him getting used to the lead around the garden and the only times he's been on the lead are to the vets, where he did pull.
Do i let him get used to being out on the lead, then in subsequent walks start to train him not to pull or do i start straight away?
If i use walking in different directions, how long on average does it take?? are we talking one walk? a few weeks or a couple of months?
I know it will differ from dog to dog, i was just wondering how much sucess people have had with this method of training

I find that the dog gets the idea pretty quickly, then gets excited and needs reminding. So it might take a short while to get him to follow, using the changing directions method, but then he might see a bird and charge towards it, in which case you have to recap with him - swerve around till he`s back following you.
How old is he?
I know some people begin with puppies by using a lure and encouragement . If this is done in the garden, you don`t even need a lead.

Thanks for the advice, Toby is 5 months.

Another option, if you've introduced him to clicker training then you could try the 300 peck method. It's got set goals to reward for so a bit more formal than the changing directions method but as a result you tend to be able to note the progress a bit more officially.
http://www.druidalegsd.karoo.net/300_peck.pdf

Otherwise I'd just say keep at it, consistancy is the key but dogs vary in how quickly they get the hang of things.