Oh I love Legoland! We took our 4yr old and nearly 2yr old at the beginning of the summer.
My top tips (forgive me if they've been said!)
Don't attempt laser raiders straight after the pirate show. Everyone heads that way and it's the longest time to queue.
Head back to your favourite ride about 25 mins before the park closes. We went straight through on Atlantis and then straight through again. We were the last ones of the day.
And try to sit towards the front of the submarines... the back doesn't have as many windows!
Unless you are going to leave before closing time, don't bother rushing to the car park, stroll through the park, perhaps use this time to see the actual lego built stuff. The car park is always a nightmare to get out of so there's no point in rushing.
We found food rather expensive and not very good on our previous visit, so this time we took a picnic. The boys loved having a picnic and didn't feel they'd missed out. (older kids might have a different opinion though!!)
Overall... have a fab day!