Useful defaults and example for ~/.ssh/config

ssh_config

# keep connections alive
ServerAliveInterval 60
# re-use connections to the same host
ControlMaster auto
# leave connection open in background
ControlPersist 4h
ControlPath /tmp/%r@%h:%p
# use `ssh -o ControlPath=none` to disable this temporarily
# and to close this: `ssh -O exit`

# example entry
Host enterprise
  Hostname 10.1.1.1
  User picard
  Port 1701
  IdentityFile ~/.ssh/picards_id

# use `enterprise` as proxy and the local IdentityFile (shuttle.lan is reachable from enterprise)
# Warning: Use with care (see ForwardAgent in `man ssh_config`)
Host shuttle
  Hostname shuttle.lan
  ForwardAgent yes
  ProxyCommand ssh -qW %h:%p enterprise

# forward something reachable via enterprise (e.g. curl 10.2.2.2:8080)
# Use `ssh -N enterprise-warpdrive`
Host enterprise-warpdrive
  Hostname 10.1.1.1
  LocalForward 127.0.0.1:9090 10.2.2.2:8080