• Use sqlite instead of Postgres, MariaDB
• Avoid enterprise software (Kubernetes, Elastic Search)
• Only use projects with efficient programming languages such as Go, Rust, etc.
• Try to run things bare metal
• Lookout for projects which name themself minimal or light-weight

I use a Raspberry Pi 2 to self host a Dashboard written in Rust (Axum), a RSS reader called yarr and a music streaming server Navidrome. The latter two are written in Go and very resource efficient. The electricity bill should be under a Euro a month (6.4W max power consumption).