Suggestions have been made to cover why many folks out on the hill ski in a backseat position. Not much has been said about how the boots you wear
can affect this problem.
read through the above article and perform the "shell fit" check as described there on your boots to see if they fit you correctly.
if they are too big you will never be able to make up for the associated problems which come from this one issue by taking lessons
or following suggestions from folks on here. It is estimated that around 90% of those who have boots, bought them 1-2 sizes too big.
beyond the fit issues of too big a boot, there is also the need to get your COM position set over the boot sole--
This can involve the angle of the boot board, the delta angle of your bindings and the forward lean of the boots relative to the size of your calf muscle.
Boots come with a set amount of forward lean---human legs come with varying sizes of calf muscles, in saying that---it only matters how big your calf muscle is at the top of the liner---not how big it is at its greatest circumference, which is usually above the top of the liner.
A bigger calf increases the net forward lean of the tibia, pushing the knee forward and pulling the hip with it causing you to sit back. Too slim a calf allows your tibia to stand too erect (Too far back) either way your COM and fore/aft balance will be affected. There is a sweet spot---you may need to find it.