Very first basics, a good starting point:

The portrait lighting is the thing of course. There are a few lighting options, in fact, any idiotic plan you can dream up probably already has a name. :)

But in the general case, the most satisfactory and useful sure-fire variation is with a main light high and wide (maybe 30-45 degrees higher than nose, and 45 degrees wider from nose), which intentionally creates the shadows that shows curves and shapes on the subject. There are several names (like Rembrandt), but high and wide describes most of them, and is the common theme.

Do look up and know (Google) about broad or short portrait lighting, it is a choice.

And for color work, the fill light metering often should be about one stop lower than main (both at the subject), to reduce harsh shadows to be smooth pleasing gradients that show shape. You will want a light meter to set your individual flashes (regarding ratio, etc).

It is NOT just two lights on either side of camera. The fill light specifically should be very near the lens axis, to light the specific shadows that the lens sees. Without creating a second set of shadows. Fill light placed behind and just above the camera is good solution, but it could be right beside the lens.

You should be able to go very far starting there, with good results.

Softness of the light is entirely about the size of the light (the umbrella or softbox). Whether umbrella or softbox really doesn't much matter, but size matters in same way for both. Placed close to subject makes a light appear to be larger to the subject, therefore softer. Generally, the main light should be a size comparable to its distance, like a 4 foot light at 4 feet will be soft pleasing light (for the main light), and it will light about a 4 foot area. A one foot light at 8 feet won't be very soft.

Hair light and background light are nice and useful frills, NOT affecting exposure or basic lighting. Basic lighting is main and fill. Two lights just on either side of camera is NOT main and fill.

See maybe http://www.scantips.com/lights/setup/

Also, you may have used a Vivid profile for landscapes. Portraits will want a Neutral profile. Ladies want to see the correct color of their hair. Also definitely use a white balance card once after setup.

Also always keep the camera back 7 to 10 feet for proper portrait perspective. Then simply use the focal length lens that shows the view you want to see there (head and shoulders, full length, groups, etc). The 105mm lens notion simply FORCES this distance for head and shoulders (on full frame), but all portraits are not head and shoulders. And perspective is about where the camera stands, NOT about the lens used there. The ladies may not know why, but they may not like the way they look at 4 or 5 feet (too close).

Highlights on the face. A good usable guide is that the brightest facial highlight should not measure more than about 235-240 in the finished RGB picture (on [0..255] scale).