Well,whatever works. A decision has to be made about venting,gating,sprue,etc while the pattern is in the mold or after its been removed. Poking around in the unsupported sand cavity can make for a crumbly mess.
While tools can be used to cut runners and sprues,etc,pre-planning can add those features to the part pattern,so they are already in the sand,to be removed with the pattern.
With the part in the sand,still,a cork borer,or icepick,or wire can be used to probe vents down to the part pattern. Placing the vent locations blind might be tough.
Actually, wires can be placed and packed in the sand and pulled out before the mold is parted,I suppose paper straws could be used and left in place...oneway or another,vent your mold,thinking about the material flow.
Getting the material in
First,a good cast part has fairly uniform wall sections.To go from liquid metal to solid,the heat is conducted into the mold.As metal solidifies,it shrinks.
The metal cools and hardens at the outer skin first in contact with the mold.
It will be liquid under that skin as it cools,shrinks,and hardens.
Now get this,the shrink will be drawn fom what is liquid.Least resistance. So while the outer skin is hard,the tickest cross sections,is where the shrink will be pulled. You will have porosity and voids,and maybe large,brittle crystals. Plus a lot of stress.
To be continued