DC seems to have had a haphazard approach to building a shared universe with a stand-alone Batman trilogy, a new Batman appearing in the Superman sequel, an Arrow TV show with a Flash spin off, a Gotham TV show and potentially a Constantine TV show and film(?)...
...but what if they have a grand plan that will link all these properties into one shared universe?
My proposed timeline;
'Gotham' - can be the early days of Gordon, coping with moving to Gotham, joining Gotham PD and the rumours of a bat-like vigilante (so basically 'Year One').
'Arrow' - several years after 'Gotham'
'Flash' - spinoff from 'Arrow'
'Constantine' - separate from 'Arrow' and 'Flash' but can take place around this time
'Man of Steel' - (at some time in an upcoming episode of Arrow/Flash there can be reports of the carnage at the end of MoS to show that those shows have been taking place before MoS)
'Batman vs Superman'
'Wonder Woman' - a solo film that can be hinted at in 'Batman vs Superman'
'JLA' - crossover film with Batman, Superman, Wonder Woman, Arrow, Flash.
'Justice League Dark' (companion film using the same actors from the Constantine TV show)
We know Batman will be an older, established crime fighter in the sequel so this timeline shows he as been active way before any other heroes emerged. (If DC wanted to get really clever they could even have Batman be Blake, meaning The Dark Knight films occured between 'Gotham' and 'Arrow', and since then he has taken over the role...)
They could slot the 'Green Lantern' film into this timeline if they decide to keep it canon - although I think the best approach would be to keep it canon but have John Stewart take over the role from Ryan Reynolds' Hal Jordan.