Where the bath is up against a solid wall, ALWAYS hack out the plaster in the strip where the bath buts against the wall, level and bracket the bath directly to the bricks / blocksl, and fill the gaps back up around the bath with render or plaster, let it set and then tile. This makes sure the bath won't move. Don't just attach the bath to the wall without setting it into the plaster!
If the bath is up against plasterboard, you can't, but make sure the bath brackets are screwed into timbers behind the plasterboard.
Fit the bath up, tile the wall and lay the floor. Make sure you give enough time for the tile adhesive to set-off (about 6 days for tub adhesive or 1 day for rapid set). NEVER use all-in-one tile and grout - this is the work of the devil.
Once the tiles are sent and grouted, you can install the rest of the suite.