Most installation problems are not hard to fix on their own. They become hard when a step is skipped or done out of order, because the next person on the job builds on a mistake nobody noticed. Knowing the normal sequence lets you spot when the job is drifting, even if you are not the one holding the wrench.
Before the first cut
Settle the location, the power, and the drain route first, since those decide where the unit can go at all. Confirm that the supply valves ahead of the install point close fully and that the old pipe is not so corroded that a shutoff will leak. Ask who will cut the pipe and whether a bypass valve is part of the job. The bypass lets water keep flowing to the house while the softener is off, so it should be in the plan from the start rather than added at the end.
Shutoff, cut, and connect
Once the supply is off and the lines are drained, the crew cuts the pipe and connects the head and bypass. Watch for three things. First, the flow arrows on the valve should match the direction of water through the house. Second, the bypass should be in bypass position while the supply is restored. Third, every joint should be seated and secured as the manufacturer's instructions call for, with no fitting pushed on loosely. Open the supply slowly so a weak joint shows up as a small drip instead of a flood, and check each connection before moving on.
The drain line and the brine tank
The drain line should slope downhill from the valve to a drain that can take the flow without backing up. Ask whether your local plumbing code requires an air gap, and confirm it has been included if it does. The brine tank should sit level on a stable base, with the float and brine well placed so they are easy to reach for later service. Make sure the drain hose is secured so it cannot slip out during a cycle.
Power, first fill, and programming
Connect power only after the water side is complete and checked. Confirm the outlet is where the plan said it would be and that the cord is not run across walkways. Then the crew fills the brine tank, starts the unit, and sets the controller. This is where your settings sheet matters. Hardness, regeneration timing, and the clock should all match what was agreed. Ask the installer to read the programmed values back to you while you watch the screen.
The test that proves the install
Do not sign off until the unit has completed its first regeneration and you have seen it run or can verify it. Then test the water at a tap after the softener, not only at the valve, and write down the reading. Check every joint and the drain for leaks, confirm the bypass has been returned to service, and ask how often the salt level should be checked and where the salt goes.
What to keep
Get the programmed settings, the shutoff and bypass locations, the warranty terms, and the service contact in writing. The paperwork lets whoever services the unit next pick up the job without guessing. If any step was skipped, ask for it to be completed and documented before the crew leaves. If you are still choosing who will do the install, the company ratings on the home page can help you compare how companies handle this kind of startup work.