Ah, it sounds like you're describing Scoot. I've been a member for years, and while I don't use them super-frequently, I've taken a decent number of rides on them. Their safety guide is rather comprehensive; so I'd start by reading all that. A few—ok, a bunch—more thoughts off the top of my head:
- Watch out for rail tracks. Seriously. Streetcar tracks are super dangerous, can be found in the middle of the street, and I'm aware of a nasty scooter crash caused by them just in the past week. If you're near them, slow way down and be careful to cross the tracks perpendicularly. Don't let traffic intimidate you into taking them at speed and don't allow yourself to ride immediately next to them, as you risk getting caught. This will result in a sudden and painful fall. Be similarly cautious of metal plates that are used to cover the road during construction; you may need to slow to a near stop approaching some of these.
- Be careful with wet weather, both rain and the more common fog. Things get slippery fast. Especially if you're not used to riding, consider a different transit mode.
- Wear good gear and cover exposed skin. Wear decent and supportive shoes.
- Take your time parking. The only mishap I've had on one (and it was thankfully trivial) was backing into a tight space in a garage. The throttle on your right hand is live, and it's possible to send the thing flying forward when you're maneuvering, especially if you get off the scooter to finish parking. When I took their training, I was taught to always get on/off from the left side, and to be careful of anytime I put my right hand on the handlebars.
- Related to that, be careful about parking restrictions and street cleaning signs to avoid expensive tickets.
- Your instincts as a cyclist will serve you well. San Francisco drivers are, er, not particularly respectful of traffic laws and will frequently make illegal turns, pull U-turns in the middle of streets, and change lanes without signaling. Double parking is rampant. Assume everyone around you is going to do the stupidest possible thing at any given time, and allow space for that.
- Drivers often make right turns without pulling all the way to the right of the street, and they may not signal. Be very cautious passing on the right. Going along with that, watch for cyclists on the right when you turn. Just like on a bicycle, stay out of the door zone.
- The city has a large number of Uber and Lyft drivers at any given time, and they are prone to sudden stops in the middle of the street to pick up/discharge passengers. Leave adequate following distance and be very careful going around stopped cars.
- Plan your routes. If you're not a confident rider and/or extra concerned about safety, you might prefer some slower residential streets to faster-moving arterials. That can be difficult if you don't know the street grid, but some pre-planning to find parallel streets with Google Maps can help. There aren't a lot of trips within the city where mapping apps will recommend a freeway (especially during commute hours), but make sure you don't get directed onto one; it's illegal and obviously unsafe on an electric scooter.
- The scooter doesn't have a ton of power on big hills, especially under load (depending on your weight and how much you're carrying in the box). If you're moving slow, try to keep to the right and be prepared for cars to pass you. Take the time to practice starts on hills, since you'll need to deal with those at some intersections. The throttle has a cut-off when the brake is engaged, and figuring out when and how to pull up your feet takes a bit of getting used to.
- Your phone fits in the phone holder, and you can run Google Maps or Waze so you don't need to worry about directions. The eastern part of the city has a lot of turn restrictions and one-way streets, so it can be difficult to navigate without an app unless you know the area well.
- Take your time. Don't let cars intimidate you into going faster than you want to. They'll wait or go around. Most streets don't have speed limits above 25. This is all especially true going down hills, where you can pick up speed quick; keep it slow enough so that you're confident you can stop quickly. Don't rush into turns; slow down before you start to turn, even if that means the person behind you has to wait a second.
- Practice. Find an alley or a parking lot and get comfortable with everything until you're confident about driving in traffic.
I'd also note that there are a number of other transportation options in San Francisco besides scooters (which can be a bit on the expensive side compared to other options). Muni, the city's public transit system, is not the most reliable, but has extensive reach and is serviceable for many trips. BART's subway also covers parts of the city. There's also Uber and Lyft (both in solo and cheaper shared ride variants) and bikeshare (both GoBike and Jump, the latter of which is electric and the former will be again once some issues are worked out). And many trips work well as a combination of different modes, such as riding bikeshare to a Muni line. The scooters are a great tool, but they aren't always available and aren't always the best option, so I like to consider all the options on a per-trip basis. The Transit app does a good job of showing all the available services in realtime, from buses to cars to scooters to bikes, near you.