As far as cleaning tech devices, screens in any form and size pose the biggest challenge. The obnoxious trend of wiping off mobile screens with toothpaste was here for a while, but it is simply not recommended.
What you should do is take a small amount of spirit, or nail polish remover on a micro fibre cloth, which you can find in your own house, and use it to wipe the screen. If you are confused regarding selecting the right fabric, just get something similar that comes with your spectacles from the spectacle cases from the ophthalmologists.
For laptops and television screens, it is better to use distilled water on micro fibre and cleaning the outer area. The edge or the corner of the laptop screen or television can be removed with bristles of a soft brush.
Camera lenses are the most delicate devices to clean and certainly the trickiest. All you need are Q-tips, a towel and distilled water.
Soak the Q-tip in distilled water, dry off the excess liquid on the towel, and gently strike the tip on the lens in a circular motion. Use three Q-tips to get the desired results and you will be good to go! However, the water should be boiled, and then rested till lukewarm to prevent any microbial growth.
Last but not the least, it is always wise to use screen protectors and keep a micro fibre wipe handy in your bag for a quick wipe when necessary.