Recently we visited Legoland Windsor. Its well signed off of the M4 and throughout Windsor.
Legoland can be very expensive so its worth looking out for 2 for 1 deals or you can use Tesco Clubcard points to exchange for tickets and its definitely a cheaper way of visiting.
When you arrive you need to pay for your parking at one of the ticket booths which is currently £5 and they give you a pass to show when you exit at the end of the day. Here they will give you a park map.
The park opens at 10am officially most of the year round but you can enter and walk round from 9.30am. Its worth arriving early especially at busy times of the year like weekends and school holidays. I would advise starting from the area furthest away from the entrance and working your way back as this is where most of the popular rides are and if you go early in the day the queues are not too bad.
We started with the Legoland Driving School where the boys earned their own Lego driving licenses and then headed for Atlantis which I would highly recommend as it has a submarine ride where you can see real sharks, rays and fish swimming past you and when you exit the ride there is a small aquarium area with a touch pool where you can get your fingers cleaned by a shrimp !!!!
There are rides for all ages from those for thrillseekers to those that are much more sedate. The boys would recommend the log flume which they made us go on in excess of 5 times in a row but you will get soaked. If you are going any time other than a very hot day where you would dry out I'd recommend taking waterproof coats or a cheap poncho (I was told they sell them in poundland) as you get very wet on some of the rides but they are all good fun.
If you get fed up of queuing there are loads of play areas, a pirate themed show to watch, Miniland which is like a model village all made of Lego of course and various other quieter areas to explore like the Duplo splash park, a 4D Film, X Box gaming zone and various areas where you can build Lego models. These never get particuarly busy so can be a good escape from the busyness of the park. The Star Wars Lego area comes highly recommend from both boys and is a walk through area so no need to queue here either.
Legoland is a lot of fun but very expensive so I'd recommend taking a picnic to keep costs down as its expensive to eat on site. There are lockers you can use rather than carrying stuff all round the park and the staff are all very helpful and friendly. Worth a visit for any Lego fan !