The best bet is to aim for spring or autumn, when temperatures are mild enough that the city doesn't become claustrophobic (or smelly!). The famous carnival usually falls in February, as does Valentine's Day, both of which draw huge numbers of visitors. We visited at the end of February (just after these events) and found the city to be relatively quiet, creating a stunning, peaceful mood. Winter can be incredibly atmospheric (particularly if it snows), but it can also bring acqua alta (floods caused by high tides). If your visit does coincide with one, don't panic: they usually only last a few hours and the Venetians are well prepared (often with spare wellies at the ready!).
NB, please do not rely solely on this information for your travel planning.
VENICE: BY AIR
From the UK: carriers include Ryanair, easyJet, British Airways. Flights from London take a approximately 2 hours and 30 minutes.
Within Europe: try Ryanair and easyJet.
By train from the UK: take the Eurostar from London (changing in Paris). See Seat 61 for details.
FROM THE AIRPORT: On arrival in Marco Polo airport, you can take a bus or taxi to the Piazzale Roma, or travel by boat (water bus or private water taxi). Tickets can be purchased in the airport, or booked in advance. There are regular atmospheric Alilaguna boats straight to the centre. The red motorboat line serves Murano – Lido – Arsenale – San Marco – Zattere and the blue line Murano – Fondamente Nove – Lido – San Zaecaria – San Marco. This takes 40 minutes to 1 hour. If you're flying into Treviso airport, there are frequent buses to the Piazzale Roma (40 minutes).
BY WATER: Buy a 24-hour / 72-hour vaporetto pass (vaporetti are the water buses of Venice). Try the gondola traghetto (gondola ferry) across the Grand Canal.
BY FOOT: In winter - when periods of acqua alta (high waters) are likely - take wellies, and bear in mind that wheeled cases and pushchairs may be hard work.