You should take into account mainly the following parameters.

shared_buffers
work_mem
maintenance_work_mem
effective_cache_size

Aboutshared_buffers:

• Below 2GB,set to 20% of total system memory.
• Below 32GB,set to 25% of total system memory.
• Above 32GB,set to 8GB

Aboutwork_mem,this parameter can cause a huge speed-up if set properly,however it can use that amount of memory per planning node.
Here are some recommendations to set it up.

• Start low: 32-64MB
• Look for ‘temporary file’ lines in logs
• Set to 2-3x the largest temp file

Aboutmaintenance_work_mem,here are some recommandations:

• 10% of system memory,up to1GB
• Maybe even higher if you are having VACUUM problems

Abouteffective_cache_size,here are some guidelines.

• Set to the amount of file system cache available
• If you don’t know,set it to 50% of total system memory