1 - Do not under any circumstances install and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac.
2 - Follow the instructions in these two user tips: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.
3 - You didn't give the size of your boot drive but if you need additional space on it (it's recommended to keep a minimum of 80-100GB free for optimal system and application use) this portable SSD is very easy to carry along with the MBA: 1TB OWC Envoy Pro mini.

4 - use Time Machine to make backups of your boot drive (and any external drive you may have). If you don't it's like driving without seatbelts - you don't need them till you do and then it's too late.
5 - if you are considering an upgrade/update to the system or an app or a new app and not sure come back here and ask before you leap.
