Raw linseed oil tends to penetrate better than boiled linseed oil.
Hit hard enough to create a dent in the middle of the bat. Check to see if you did make a dent. Then gently knock the face of the bat around this dent to make it level. When done, you should no longer see the dent. Round off the edges. Hit with a 45 degree angle to the face. This allows the mallet to compress the willow. Start with one dent on the edge, then gently knock around it to remove it and smooth the edge out. In each case, repeatedly strike the face and edges of the bat whilst gradually increasing the force of the strike over time. Do not use the mallet on either the face or the bottom of the bat toe with the mallet.