Where is best to break the journey to make the price cheaper?

Leeds?

No, seriously, you may find it’s cheaper to travel away from your destination and then back to get a better deal.

I’ve done this a few times, only thing is it makes the journey longer.

Have a glance at this, it may well help you decide.
http://www.moneysavingexpert.com/split-cheap-train-tickets/

Get a ticket from Sheffield to Doncaster, and another one from Stevenage to Kings Cross and hide in the bog between Donny and Stevenage.

Those split ticket sites are good but not fool proof. They offer split ticketlook at the standard route and divert from that, they may not consider going in the opposite/alternate direction.

That is of course if you are happy to consider

Example.

Im near newcastle, so local station to the south, routed via newcastle on all ticket websites = ~£120 single.
Split sites, came up with ~£100 (again via newcastle).

However, Carlisle to South, standard ticket site was £32, plus the £7 to get to carlisle from my local station.

This was all same-ish departure time, and same travel time (obviously changes etc.

Always worth looking at the costs for the whole day on trainline etc, ‘cheapest’ is only cheapest for times shown, not cheapest for the day.

There’s an odd anomaly where I live. The train goes Stafford – Penkridge – Birmingham. As you would expect, Penkridge to Birmingham is cheaper than Stafford to Birmingham.

Because some trains don’t stop at Penkridge, that cheaper ticket goes via Stafford.