For pictures I take on my phone, I attach the phone to the Mac with a USB cable, and then open the Image Capture app (I have a link to it in the Finder sidebar). Then I click "Import All" and all photos from the phone are copied to the Pictures folder.
I plug my Nikon's CF card into a SanDisk card reader on a USB port. The card shows up as a volume in the Finder, and then I drag my photos to a folder on my hard drive. (Rather than using Image Capture or any other program.)
I have a Sony camera that sends its pictures to my Mac via WiFi. This works fine.
No matter what device took the pictures, I check the files using Quick Look to make sure they got onto the disk, before I delete them from the device.
I have scanned old pictures, both slides and flats, using an Epson 4490 scanner, and had good results. It takes time though, between 5 and 10 minutes per picture.
I sent hundreds of slides to ScanCafe.com, who scanned them to disc in India at a low price. This was very satisfactory.
I try to remember to make the original files read-only just after I copy them to the Mac. The idea is that my original should never be changed.. always work on a copy, so if I screw up or change my mind, I can recover.
Never have only one copy of a file you care about: back it up. I have a folder which contains all the original picture files from the camera, in subfolders named things like Nikon8, Nikon9, etc. When a folder gets near to 650MB, I burn it to CD-R and start a new one, in addition to all other backups I do. If I take a trip and have a lot of pictures that go together, sometimes I will burn a DVD+R or even a DL disc. But the idea is to have a read-only backup copy before I start changing things. I took a really great picture in 2001, and while trying out filters in Photoshop, accidentally hit SAVE, and destroyed the original.
Years ago, I wrote up a useful cookbook about how I prepare photos for web use. It is still a good start.
I look at newly loaded pictures with Quick Look, and if they should go on my web pages, I open them in Adobe Photoshop. I straighten and crop, and adjust curves, and then run a standard saved action that changes the image size and runs Smart Sharpen. Then I save the result as a JPG using Save for Web. Usually a quality of 30 to 50 looks just fine. The input picture is usually around 3MB; after processing, I end up with a file around 50KB. I drop the converted pictures in a folder and edit a file that has a caption for each file. Then I invoke software I wrote to generate thumbnails and run a Perl program to regenerate the album web page. (Thumbnails are generated using the "convert" command from the ImageMagick package.) Each album page shows the thumbnails and can pop up a view or slide show of the converted pictures.
Adobe no longer sells Photoshop: it rents its products for $20/mo/product. Look into Affinity Photo as an alternative to Photoshop, and Affinity Designer as an alternative to Illustrator. GIMP is a free alternative to Photoshop. Acorn is another photo editor for Mac, costs $29.95 one time. I have been trying out Affinity Photo and still find it harder to use than Photoshop.
I copy pictures into the Photos app for display on the Mac. (I used to use iPhoto, which was superseded in Yosemite.) The Mac's screensaver will display a Photos album, and that's how I set up our living room computer to show snapshots at random.
On the living room computer, I have thousands of pictures in Photos. For each picture I add, I edit and straighten and crop it if necessary. Since the display is an HD TV, I try cropping to 16:9 if the picture can stand that: doing so will eliminate black space at the sides or top of the picture. Then I try the "enhance" button to see if this makes the picture look better. If not, I may try individual functions from "Adjust" but I don't spend a long time on it. Some pictures are improved on our TV by using the "Definition" and "Saturation" sliders. Depending on the camera's settings, it may also need a hit of "Contrast." I created a Photos album called "screen" and add pictures to it if they should be in the random screensaver. (I patched the OS to have each picture stay on screen for 30 seconds instead of 3 seconds.)
I encountered problems with iPhoto: crashes and database corruption, missing features, a general closed-garden approach, a confused and poorly explained interface metaphor that provided "Events," "Folders," and "Keywords." A photo could be in only one Event, but could be referrred to by many Folders: editing the photo changed its appearance in all Folders. The Photos application that replaces it seems to have its own list of deficiencies.
When I installed Yosemite, the installer created a Photos database from my iPhoto database.
So far, I am disappointed in Photos. Many features of Photos seem to be inconsistent and hastily assembled, and there is little documentation.
The concept of "events" in iPhoto is no longer supported in Photos.. your old iPhoto events are saved as a folder that contains other folders, but new imports do not create events. Instead, Photos has a new feature called "Projects" and this is where you create Books, Cards, Calendars, and Slideshows. "Keywords" are still present, as are location display and face recognition.
Picture editing in Photos is similar to iPhoto, once you find where the controls are hidden. Hint: double click a photo, click "Edit," then click "Adjust" and then click "Add" to enable the hidden controls.
Pictures that you adjusted in iPhoto and then imported to Photos can look peculiar, and need to be re-adjusted. They all seem to have a sharpening effect added to them.
Some operations in Photos take a while to complete, such as. Once you initiate one of these operations, there is no visible indication that it is in progress and no indication that is has finished.
Photos also has some picture corruption issues on my Mac Mini: sometimes a rectangular selection of an edited picture is replaced by garbage or a black box. The original is undamaged. I have seen this in both Sierra and High Sierra. Usually, re-editing the photo and re-saving it fixes it.
Slide shows in iPhoto were limited. In Photos, there are two ways to display a slide show of a group of pictures: you can right-click on a folder name and select "Play Slideshow", or you can selectwhich will create a "Project". Folder slideshows play music during the slide show, and there is no button to turn the music off or control inter-slide timing. You can turn the music off for a project slideshow, by clicking a music-note icon on the project, and hovering the mouse over the selected music until an invisible button with an X becomes visible, and clicking it.
In OS X El Capitan, the ability to add "extensions" to Photos was provided, and there are some available in the App Store. A few things I would really like:
There are programs like Picasa, Adobe Bridge, etc that help you manage your collection. I have tried a few of them but don't use them consistently.
Another thing I have not gotten into is shooting in RAW format. This makes bigger disk files but would mean I could adjust a lot of things like white balance later. The real expert guys who spend a lot of time making their pictures perfect shoot RAW. It is especially important for photos that will be printed on paper.