First, Define Your Goal:

Focus and meditate before you begin. Generally the more specific you can be about what you really want to achieve, the better your results are likely to be. 

Consider the possible implications of what you think you want—be careful what you ask for. What happens when you get it?  

Stick to one simply-stated goal per spell. Diffusion, generalization, and complexity will weaken and confuse the outcome. If, for example, your mother needs relief from depression, and you are working with someone whose mother is recovering from a hip replacement, and another person whose elderly mother is probably dying and needs whatever spiritual support she can be given, there you have three very different spells. Do not succumb to any temptation to save time and energy with one spell for everybody's mother.

Also, in order to focus your will to the extent needed to succeed in a spell, you have to care about the outcome. I was once with a group of people who were discussing the way to respond magically to a rapist, and the suggestion was made that one should focus on healing the rapist so that he would stop committing crimes. 

This is noble and generous, but probably of little efficacy for the simple reason that, in a case where someone you care about has been raped, the welfare of the rapist is probably low on your list of concerns. You probably care about stopping him somehow, and helping your friend recover from the trauma. That makes two spells--binding the rapist, and a spell of healing and empowerment for your friend--probably enough work for one night.

But it is also possible to inhibit the power of a spell by wanting something too much. This is why many witches can do more effective spells for others than they can for themselves. One possible explanation is that, when wanting something terribly, you inadvertently create mental images of the thing you fear--that it won’t come to pass, and these images may contribute the the failure of the spell.

In most cases, baneful magic is discarded when you really become specific about what you want--for example, you probably don’t care what happens to the person who took your wallet so much as you want to get the contents of the wallet back. 

Sometimes bargaining seems to work in magic--let go of the money that was in the wallet, but work to recover the documents in it, for example. 

Many Witches arrange with their cars not that they will never break down, but that any breakdowns will occur at times and places when the problem will be manageable.