Opening Vim help in a vertical split window

:vertical (vert) works:

:vert help

You can also control whether the window splits on the left/top or the right/bottom with topleft (to) and botright (bo). For example, to open help in the right window of a vertical split:

:vert bo help

This command should do it:

:vert help

Dynamically open help windows at the top if there's more than one window in current tab, or on the right, if there's only one window:

if winnr('$') > 2
    wincmd K
else
    wincmd L
endif

You'll need to place this in ftplugin/help.vim or use it with an autocmd, e.g.:

augroup my_filetype_settings
autocmd!
autocmd FileType help if winnr('$') > 2 | wincmd K | else | wincmd L | endif
augroup END

I settled on the following:

" Open help in a vertical split or a new tab. 
augroup my_help
    " Remove current group to avoid double runs
    autocmd! 
    " If a help buffer is opened then try to move it to the right. If now it
    " doesn't fit help text (78 chars) then move it to a new tab.
    autocmd BufEnter * if &filetype == 'help' | wincmd L | if winwidth(0) < 78 | wincmd T | endif | endif
augroup END

It works for me in both vim and neovim. FileType help doesn't work in neovim if I reopen help because the help buffer remains hidden in neovim while vim seems to unload it.

This is what I use, taken from docwhat's answer. You can change values to your liking.

function! MoveWindowToRightOrNewTab()
    if winwidth(0) < 165
        wincmd T
    else
        wincmd L
        vert resize 85
    endif
endfunction

" Open help in a vertical split or a new tab.
augroup HelpWindowOnRight
    " Remove current group to avoid double runs
    autocmd!
    " If a help buffer is opened then try to move it to the right. If now it
    " doesn't fit help text (80 chars) then move it to a new tab.
    autocmd FileType help call MoveWindowToRightOrNewTab()
augroup END