1. Gather insight(s), which include the client's objectives and a competitive analysis. Your solution is dependent on the initial input used to guide it. Know your mediums thoroughly, too. Meet with a client, establish a relationship. You'll be dealing with a lot of narrowed perspectives: Your client, the market and any other estranged opinion(s) that may need to see the work. The relationship is critical. You're part of a larger team, even though you may be the wrist, there are many heads.
2. Iterate, but keep it collaborative–at the least, without driving yourself insane. Be confident in what you present and provide well-reasoned and rationale explanations. Some clients see it, others need to hear it. A good presentation supports both parties.
3. Establish timelines, milestones and cost of everything before hand. Granted, you can't scope a project without knowing the details, but once you've figured out what the project requires–forecast a timeline. You would be surprised in how easy it is to lose money at the end of the year. Your client should be aware of the time allocated for every step. Including a set of guidelines for revisions or when/if a project exceeds the initial launch date. Also, don't be afraid to implement a kill-fee.