Lowering your Bike.
Many motorcycles, especially standards and sport-touring bikes, come with seat heights of 31 inches or higher. It's definitely a factor to consider when buying a bike.
If your bike is a bit high, you'll have trouble getting your feet flat on the ground while stopped. There is a safety aspect to that. It contributes to the number of low-speed accidents, and dropping your bike on a busy road exposes you to risk.
Some BMW bikes have a seat lowering kit as an option. Many touring bikes have some level of seat adjustment.
If not, there are things you can do. Check out your bike model forum for advice on the subject.
Adjusting or Replacing the Seat
Consider first, the least intrusive option of working on your seat. The least expensive way is often replace the foam in your saddle, there's a how-to here. (it is about two thirds down the page). You can also buy a new seat or have it worked on by an upholstery shop. The owners forum for you bike might have suggestions for things you can do with the seat mounting hardware to make it lower.
Seat customization might include making the front part of the seat narrower. There's often not much scope for making the foam thinner, although replacing foam with memory foam can do that. A narrower saddle front cuts the distance from your arse to the ground, and does the job of allowing you to flatfoot the road easier.
Check the top view of potential replacement seats to get an idea of their lowering potential.
Some seats come with rubber buffers and/or spacers under the saddle, which can sometimes be removed or cut down. Check your bike forum for these details.
Lowering the Suspension
Your bike mechanic, owners forum or shop manual will provide information on adjusting the bike's suspension to make it lower.
This should be considered a last resort, especially for cruiser-type bikes with low ground clearance.
Modification kits are available for many bikes, which may be 'dogbone' links or replacement parts for the shock, and it is theoretically possible to shorten the spring. These kits will affect the bike's handling and you might want to check your bike forum to see that experience other riders have had.
I found that having a custom rear shock made by a reputable manufacturer to your specifications is often the best way to lower the bike while maintaining good suspension performance. You can get stock replacement shocks for some bikes. Again, do what you can to find other riders experiences and compare notes.
This sort of work is beyond the mechanical capabilities of most riders, so you'll need to find a mechanic you can trust to install either the new shock or the modification kit.
It is usually essential to shorten the kickstand when you have your suspension lowered. The bike will stand up very straight (or even lean the wrong way), and you'll drop it when parking on uneven ground.