In two words: positive mindset.
I used to do this return journey in WT on BA11/12 about ten times per year, but, thanks to FT, am usually on another oneworld airline in more comfort now. Sadly, there's still the odd trip down the back to SIN that I have to make on BA. I would also advise you to pick up a selection of snack and drink options at Boots in advance, eat a 5 course meal in the CCR, and certainly move across to 70A. That seat (along with 70K, 80A, and 80K on the A380) is one of the four best WT seats on the entire BA fleet. As others have mentioned, noise-cancelling headphones and a bag you can rest your feet are also smart ideas.
You may well get upgraded to WT+ or even straight to CW as a GGL (especially if you're travelling at the weekend), but DEFINITELY don't allow yourself to fall into the trap of constantly updating the app like a loon whilst tucking into your G&T in the lounge!
Hope it goes well.