Here are some of my stone projects,
All the stone used here is schist which comes from various sites in Otago, New zealand.
These projects have been built 25min Drive from Queenstown which is a world famous tourist destination in NZ.

Dry stone free standing wall.

Use a batter of 15 deg,
Follow String lines to keep wall strait.

Step 1: Pizza Oven Area.

Natural stone paving on ground.
Veneer work around pizza oven.
Walls and seating in dry stone with top slabs mortared on to keep them solid.

Step 2: Dry Stone Retaining Wall.

Best to keep a 15 deg batter with dry stone retaining walls to hold the weight of the soil behind.
Use a stake at each end with a string line to keep strait.

Step 3: Veneering

Here's a veneer wall with a circle window going in.
Make a template which you build the window around. leave it in until the wall is built, the top of the arch will fall if there is sloppy workmanship.
Keep quite a dry mortar mix so it is strong.
Use a string or large square to keep all stones pointing to the center.
Try to keep all mortar joints the same and horizontal lines strait in the rest of the wall.
String lines are also important to keep the wall strait.