I am a beginner myself; so correct me where I am wrong. This post is being composed from the notes that I prepared for doing portraits while reading manual and articles / videos on the net. The terms I am using apply to Canon DSLRs; other vendors must have similar features.
Mode
[INDENT]Use Aperture Priority mode; it will allow you to select the right aperture that is important to keep the subject sharp while blurring the distracting background and allow you to select lower ISO (for lower noise); by controlling aperture you can work in lower light (if your lens allow this)
[/INDENT]Shutter Speed & ISO
[INDENT]Keep an eye on shutter speed being selected in Av; it should remain 1/60 or faster to reduce camera shake. If using VR / IS lens; you can click with bit longer exposure (1/30 or may be 1/15) but you have to ask your subject to hold. Always manually specify the ISO; and if required bump up the ISO upto 800 to achieve proper shutter speeds. The modern cameras dont generate noticable noise upto 800 ISO.
For child giving expression; you might need to switch to Program or Manual mode; as shutter speed needs to be 1/125 or 1/250; if required use flash to achieve this.
[/INDENT]Lens
[INDENT]Using zoom; you can achieve blurred background effect but you should keep close distance to the subject; otherwise you will not get narrow depth of field.
[/INDENT]Metering Mode
[INDENT]Generally Evaluative Metering Mode (the mode that evaluate entire frame) works fine. In very light or dark backgrounds; this mode might not work perfectly; use Exposure Compensation or change the metering mode to Partial Mode; where it will use the center area of viewfinder to get the exposure info.
[/INDENT]Focusing
[INDENT]Always focus eyes; eyes should remain sharp. Use One Shot focusing mode and select single focusing point. If subject is moving (kids etc) use Auto Exposure Lock to recompose. Zoom into subject; focus; AE Lock; recompose and click!
[/INDENT]I use One Note for taking notes; its the best addition in Office lately; do check it out!