You need to find the subs you want early in the process---during the planning if possible. Be aware some contractors will try and get by with less than agreed on work, simply because a home owner is a one time customer and usually has very l;ittle idea of preferred or proper mateiral and methoids of construction.

A lot of people have attempted being their own GC, and found hiring a reliable one is a much better idea.

Are you adding an addition to your house?

First, contact the local codes office to see if your plan is within codes. A drawing (hand made) of the lot, house footprint, and new addition footprint should suffice for the initialdetrermination. No point in hiring an architedt if the addition is not within codes.

Basic process:

Plans.
Dig check.
Permit.
Excavation/footings/foundation. If any plumbing needs to be installed, the plumbers may need to add lines before the foundation work. Concrete will need several days curing time before framing.
Concrete flooring poured(if needed.
Inspections as required.

Framing: flooring support and sub floor. Walls and roof framing. Roofing can be installed(any vents should be installed in the roof during framing---not added later. Exterior sheathing installed. Windows and doors installed. Any reconfiguration of exterior walls that are now interior walls done in this section.
Inspection.

Electrician does rough in. Any HVAC work done. Plumbing rough in done.
Inspection.

Insulation/drywall installed. Exterior siding/painting done.
Inspection if required.

Painting/paneling/interior wall/ceiling treatments.

Finish electrical and trim carpentry.
Baseboard installation depends on type of flooring. If flooring will be wood/tile, installing baseboard is usually done after the flooring. If carpet, the baseboard can be installed before the carpet.