I found that riding with locked elbows helped me when first riding an upright solo trike, steering with my shoulders. It seemed to work but was tough on my arm muscles. That sort of advice is probably a waste of time for your tandem trike, given you have spent some time on a solo trike without too many dramas.
You will have to think about how much you need to lean out on faster corners though. The 'triangle of support' is quite narrow for the captain and much wider for the stoker. Tandem trikes have a slightly wider track than solos but captains can be restricted in how far they can lean out by the stoker's bars.