The most important setting is the option to add tag, color class and rating to IPTC/XMP data for all photos. This will maintain Photo Mechanic's 'soft edits' through editing in other applications.
Last but not least, I suggest opening up both apps and then make the Color Class colors and labels (on the General tab of Photo Mechanic's Preferences dialog) match your Lightroom settings.
Then use Ingest to download your images to a Primary destination and a Secondary destination. Applying an IPTC Stationery Pad is also a good idea. Start with only the fields and information that are applicable to the entire set of photos that you're ingesting. Things like the Photographer, Caption writers, City, State, Country, your contact information, and copyright are often common between all photos. Using Photo Mechanic's 'variables' can be a real time-saver here. For instance in the Copyright field, you can put something like:
Copyright (c) {year4} your name
into the Copyright field. When you apply the IPTC Stationery Pad to your photos the year that the photo was taken will be used in the Copyright field for each photo.
You can also rename your photos during the Ingest if you like. You can also do the renaming later if you prefer, or do no renaming at all.
If you setup Ingest to open Contact Sheets while the images are being downloaded you can begin working with your images as soon as they begin to appear. When you put your mouse cursor over the images you'll see four icons, two of which will allow you to rotate your images 90 degrees, and one will bring up the IPTC Info for an image (it looks like the letter 'i'). The last icon will preview your images.
While in the Preview window you can view your images in fairly rapid succession by pressing the 'right-arrow' key. If you want to zoom in on some details in an image, hold down the Command key (or Ctrl key on Windows) and click on the area of interest. It will zoom in at your current zoom level (by default it is 100%). Command-click (or Ctrl-click on Windows) again to zoom back out. The 't' key will toggle the tag checkbox, and there are many more keyboard shortcuts for Color Class and Rating your photos. Check the manual for details.
What many people do is make multiple passes through their images, the first one to just get rid of any photos that are obviously of no use, then make another pass to rate or classify the images.
Once you have culled your images down you can then switch to using Lightroom to make any RAW adjustments and if you have Lightroom just reference the photos where they reside then you can switch between the two apps to make use of each app's useful features.
Hopefully this will help you get things started and get you familiar with Photo Mechanic.
-Kirk