One can also use the leverage of the trailer, by lowering the tongue as much as possible, then securing the stern, with cribbing/jacks on the transom, or mid line transom, then raising the trailer tongue to give clearance aft. You can then use hydraulic jacks for ward under the keel. and jack the forward part of the hull up--putting the trailer at neutral, and giving room for working between the blocks and bunks.
Some will remove the trailer--doing this requires using cribbing in several places forward.
You want the main weight to be on solid areas--for example the transom/keel area. You want to balance the boat with jack stands, but not take the weight of the boat on jack stands. Always speed the force out on the boat, never put a metal jack top on the hull.
I prefer to use wooden cribbing. Concrete blocks can be a problem--and break. I have some auto jack stands, rated for 4 tons, and used wooden cribbing of 4 x 4 and 6 x 6.