Long ago I found a tip (once on vim.org, now on wikia, apparently) that I’ve stuck with. Remap ctrl-[hjkl] to navigate splits. It has served me well.
" Use ctrl-[hjkl] to select the active split!
nmap <silent> <c-k> :wincmd k<CR>
nmap <silent> <c-j> :wincmd j<CR>
nmap <silent> <c-h> :wincmd h<CR>
nmap <silent> <c-l> :wincmd l<CR>