Building neat makes for easy mods and trouble shooting down the road. It takes a little more time but it pays off in the end.
Keep all lead (wiring) length to a minimum, especially the grid wires, if you have parasitic oscillation (like motorboating) check the grid wire length.
Pay attention to how the grounds are layed out. The filter caps that feed the preamp section should ground near the cathode resistor grounds for that section. The main power filters and screen filters should ground in the same place, where the output tube cathodes are grounded. This will help eliminate noise, hum and oscillation.
If your power transformer came with extra center taps that are not called for in the schematic, cut them off or coil them up and cap the ends, do not wire them to ground. If the PT didn’t come with a center tap for the heater circuit (6.3v), don’t forget to add an Artificial Center Tap for hum reduction.
If your new build does not work, chances are, it’s a disconnected or miss-connected lead or something mechanical like that. Check the entire circuit over for bad solder joints, missing grounds, grounds where there should not be one, before you decide to re-engineer the circuit or start replacing parts.