Thought I'd pop on here to get some information as I'm finding it really difficult to figure out how I'm gonna get to the Excel. I'm flying in from Ireland and I've never used the trains in London before. 

I want to find the fastest and easiest way to get to the Excel, so I was going to take the Heathrow Express to Paddington Station, then Paddington to Oxford Circus, get on the Central Line to Bank, and then Bank to Prince Regent as Custom House is closed? I also read that I can't go straight from Bank to Prince Regent so will I have to change again before that?

Plus, I heard I can buy a day ticket for trains which would be preferable than buying each time. It seemed like a lot of trains for someone who doesn't know London well so please let me know if you have any advice! Thanks in advance!