You could start with the LEA or Borough website to find out the application procedure timescales and details of local schools. For state schools you could phone directly and express an interest now but you'd still have to go through all the application porcess with everyone else nearer the time, probably some time during the academic year before the September she'd start Reception. Registering now, assuming they are even inetrested enough to take your details, simply means you'd be sent information direct at that time.
It would be worth checking what the relevant criteria are for these schools (proximity of home to school, siblings already attending, practicing specific religion etc) as if they get oversubscribed by children living closer to them already for example, it may leave you with less real choice. There is a bit of a row brewing over selection criteria (ie. where children of staff take precedence over more local children) for some schools atm and this may well have more of an impact in future years as Govt seek to standardise it more.
hth