In a larger project your success will depend upon your concordance to the appropriate strategic plan for your company. This is a fairly sensitive and deep subject: nothing seems to be as politicized in a company as much as the knowledge and implementation of its strategic plan. Many of the decisions and tradeoffs that you make very early in the architectural design will depend however upon a firm understanding of how your company will spend money, invest, and hire people across a range of various timeframes.
To further complicate matters once you have this wisdom, even though you may use it to guide system design decisions, it may still be in your best interest to safeguard your insight as private. High diplomacy may be in order.
To reach this firm foundation you need to understand your company, its finances, the industry in which it competes, and your direct competitors. You can research some of this through public sources, but you will still need to rely on the experience of the smarter and more senior employees for their knowledge.
Most people will be happy to give their counsel and experience if you establish a non-confrontational and supportive friendship with them. You also need to understand and appreciate the nature of their advice, and be thankful and willing to give them public credit for their ideas and contributions.
Most companies (and industries) follow a natural cycle of growth and decline. Even companies approaching the end of their utility however can still keep folks gainfully employed for a short while; under such circumstances you will certainly focus your approach more on quick results than long term maintainability, yet you still need to proceed in a courteous and professional manner.
Finally, remember to always balance your decisions with your innate sense for what is the right thing to do.