In my career I have found that the ability to work well with others, show empathy towards their needs, and being trustworthy have done more to help me be successful than being overly reliant on tools such as pert charts, resource loaded histograms, and quantitative risk analysis documents.
When managing any size project the project manager needs to focus on what is most important to that project's success. Only you, your sponsor, and stakeholders can answer the question of what is most important. Is the most important thing getting the project done on time, coming in at or under budget, delivering at a high level of quality, or having a big WOW factor? (See Tom Peter's – “The Project 50” book for more on the WOW factor). You must decide what the Project “Driver” is before you begin your planning.
Remember, don't get caught in the trap of believing that if you meet your Time, Cost, and Scope objectives your project is a success. If your users and/or sponsor aren't satisfied with the project's results YOUR PROJECT IS A FAILURE! Every project needs a project sponsor, charter, a budget, a realistic agreed upon schedule, competent resources, a list of valid assumptions, a list of the project’s constraints, dependencies, and people assigned to your team that are dedicated and personally committed to seeing the project succeed. However, you as the project manager must have the trust of all stakeholders and demonstrate that your are committed to doing your best and delivering on your promises.
Without the trust of your peers, management, and customers your project management career is doomed to failure.