AI7PM gave some good advice.
Be wary of YouTube and "Amateur Radio Expert" installs. A lot of the information out there is not only wrong, some of it is dangerous.
The radio is a heavy chunk of metal mounted inside the passenger compartment. It needs to be secured well. Velcro, double sided tape, small sheet metal screws, bungi-cords, etc. are NOT appropriate installation methods. Your first step should be finding a way to properly install the radio chassis. It needs to be well secured. You need to mount it in a place where it will not block your vision, will not be in the way of airbag deployment, is not exposed to direct sunlight, and you can still reach it easily. That will entirely depend on your vehicle.
I've always through-bolted mine, that is I locate the mounting bracket, drill through the underside of the dash or other location, and fabricate a backing plate that has holes that match up with the bracket. The backing plate gets put on the other side of the mounting location, and usually 1/4" x 20 screws with locknuts, washers, etc. get passed through the bracket, dash and backer plate. This will keep the radio secure on bumpy roads and prevents it from coming loose in an accident.
Your antenna is the most important part of the install. If you are not willing to properly install an antenna, you should probably reconsider installing a radio. Compromise mounts and cheap antennas will lead to compromised performance. Don't spend $300 on a radio and then hook it up to a $20 antenna and expect it to work like a $300 radio.
Permanent mount NMO dead center in the vehicle roof is best. Anything else is a compromise. Yeah, there's other options, but they have drawbacks. Use a name brand antenna. Avoid amateur/hobby grade antennas. Avoid the low cost Cheap Chinese Antennas.
Power is important, too. Do not cut corners on your power feed. Do not tap into existing vehicle wiring, that's asking for lots of issues, not the least which is RF interference. The positive power needs to come direct from the battery. Negative needs to be grounded to the body near the radio. I've often added a chassis ground strap from the radio chassis to the vehicle sheet metal. Relying on long negative power leads or ground through the antenna mounts can be problematic in some installs.
It's a big step, and not easy. As you've discovered there is some totally useless info out there on the internet. Some of the "internet expert" installs I've see are truly horrifying. On the other hand, it's not really that hard to do yourself if you've got some basic skills. There are some vehicle dependent things you'll need to sort out, but we're happy to help.