I do my meat sauce first, make it all up with the tomatoes, puree onions, garlic etc.. let it simmer for about 10-15 mins.
Then I layer it into the lasagne dish, sauce on bottom, then raw sheets, then cheese sauce... and so on, finishing with cheese sauce on top. make sure all the sheets are covered, because sometimes they peek out and go all hard and crispy.
I cook mine the first night, we eat it... then I just leave it till the next day and I reheat it for about 15 mins at about 180 degrees?
xx