Tips to save gas in solidity?

Pack struct variables
Organize storage variables to fit them 256 bit/32 bytes slots. But remember to use them together in a function otherwise, SLOAD 2100 gas will be charged multiple times, there will be no benefit of HOT load from storage.
Use Immutable and constants ( constants are stored as part of byte code)
When deploying multiple contracts as clones use minimal proxy pattern
Use calldata & memory where possible
Use unchecked {} when you are sure there is no overflow or underflow
Use custom error() instead of require or revert when possible
When you use require use smaller message lengths
Use events to eliminate the need for storage variables
Use ++number to increment
Store data in memory which needs to be read frequently, such as array.length