Scissor jacks are relatively safe for emergency use (as in, low duty cycle use) such as changing a flat. For prolonged work or frequent use, alligator jack + jack stands. Particularly when working on brakes or suspension parts.

The thing that people forget is to put wheel chocks on the other tires. For example is when servicing rear tires on a rear-drive vehicle. Walang lock yung front tires so it's critical that they are chocked.