It is recommended that you practise hitting the cue ball up and down the spots to achieve consistent results. Once you have consistent results, the next challenge is to be able to hit the object ball in the correct spot. There are many methods to help you work out the correct contact point, but I recommend the following.
Step 1 : Start by removing the old tip with a sharp knife (stanley blade). Make sure all the old tip and glue are removed. Use the knife to get the ferrule absolutely flat. Do this by using the edge of the blade and gently turn the cue while applying slight pressure on the ferrule.