Protecting the electric components from water is a must, especially if you are living in a rainy area and intends to ride your electric bicycle under such weather conditions.
The sealing of the controller, motor, battery and console have to prevent any water from getting through.
Some system are water resistant but not water proof. There is a miss conception about this terms. Usually, what it means is that water resistant sealing will prevent water from getting through but in heavy rains water may get through. Just water proof systems offer the maximum protection. Before going for your first rainy ride, be on the side, and check what your e-bike is aimed for.
Before installing a conversion kit on your own bike you should check what is the condition of the bicycle.
Don't be tempted to put a motor on a too old bicycle which makes grinding noises when moving. The least you should do is to check with a professional mechanic if the bicycle will be able to withstand the "trauma" of adding a conversion kit over the long haul. Check your bicycle for visible and not so visible cracks, material composition and condition.
Think about putting a Porsche engine inside a Daihatsu Sirion, It just doesn't make sense. The same here, low quality bicycle won't be able to withstand the high pressures and forces that caused by the motor. It just doesn't suppose to do so. You are probably risking yourself too much and your old bike can literally get broken while you ride.
Electric bikes have better acceleration and can maintain a higher average speed then conventional bikes. They are also heavier.
Therefore, using above average quality bicycle parts is very important if you want to minimize the change of an accident or an injury.
Before every trip check all connections and hinges and make sure they are in good condition. Do not use the electric bike if one of the hinges or connections are loose or broken until the problem is fully solved.
There are a couple of other aspects that worth considering especially when dealing with electric bikes. I advice you to enter the bicycle parts page to read further about different bicycle parts and get more tips about safety considerations.
Make routine check to ensure correct air pressure in the tires. And remember that small wheels losing air relatively quicker so check air pressure frequently if you your e-bike has small wheels.
An electric hub motor has a much higher torque and therefore you will most likely have to use a bolt-on axle and not a quick-release wheel. If you have a rim that you love, there's a good chance you'll be able to build a motor into it. However, the axle is going to have to change if you're using a hub motor.
Hub motors put high pressure on the bicycle forks. Therefore, steel forks are recommended; aluminum forks can cause for the bending or even breaking of the drop-out.
If the brake lever feel too lose or to firm, don't use your e-bike until you fix the brake lever or replace it if necessary.
The extra stopping power that the disc brake offers over rim brake comes in handy because of the added weight of the battery and motor.
Check your e-bike frame loading capacity. Meaning, the amount of weight you can put on it which still considered safe. Also, for example, you can usually put much more weight on a rear pannier rack vs. the handlebar.