I've done 2 houses same way dad did our old home:

This all presumes your house has crawl space or basement, not a poured slab. It also presumes your house is not J-bolted to foundation, as modern code requires. If the J-bolts are accessible, you can still level a house.

You'll be leveling the main floor; rest of the house comes up with it. Your tools are an Ellis SJ-4 Screw Jack, 4x4 post, misc small tools (carpenter level, hammer, nails), and an assortment of wood blocks, spacers, and wedges to shim the house up from the foundation.

Use carpenter level to find highest point of house floor. That's your datum point; you'll be jacking/shimming rest of house up to that level.

Under house, find main structural beams; they're big, heavy, level, and lower than other structural beams. Main structural beams rest on perimeter foundation and individual, free-standing vertical posts.

Assemble your screw jack and 4x4 post. Choose a too-low main structural beam and associated support point (perimeter foundation or vertical post). Find accessible ground space next to the associated support point.

Measure height from ground to structural beam. Trim house jack post to fit, and put your house jack next to associated support point. Turn jack screw until firmly in place.

Now here's the real secret... DO NOT tighten jack any further. Wait until tomorrow. As house cools overnight and warms in the morning it creaks and groans and resettles itself naturally. It will readjust itself to your house jack, lightening pressure on the jack.

Retighten jack firmly again each day, and house will gradually raise itself up. Gap will appear between main structural beam and house foundation/supports. Fill this gap with wedges and shims.

Proceed around your underfloor space, jacking and shimming. It'll take a month or two. As shim stacks get too thick, replace them with larger blocks. When floors are all level, nail spacer stacks into place with removable double-headed nails.

Store your house jack somewhere dry so it'll still be usable if needed again.

If you're impatient and use heavy jacks to jack everything up level at once, your house will stress, your house frame will skew, your interior walls will crack, and you'll have to patch and repaint.

If you are patient and let your house settle naturally, everything will come up square and level. Old cracks will close, and no new cracks will appear.