If you use, say, Adjustments, Layers, and History often, keep only those visible. Start by making the Histogram less prominent. Grab it by its tab and drag the tab to the column of small buttons to the left until it docks. Then go to the Window menu and uncheck Navigator to hide its panel. This will leave you space for lots of layers. If you refer to History often, go to Window > History to show it, then grab its tab and drag it down next to the Layers panel. There's no reason for the main toolbar to be on the left if everything else is on the right. Drag it over to join the rest.