If you've been coding awhile, you know how things are supposed to be done right:

• Documentation standards strictly enforced
• Code reviews
• Design and analysis taking roughly 1/2 the time spent developing the product
• Proof-of-concept of any components with unknown or risky implementation issues
• Proper documentation of abstractions, including class diagrams, sequence diagrams, and other tools from the UML toolkit
• Full specifications, preferably with use cases, cross-referenced and in a format that your coders can easily understand and absorb
• Iterative development cycles
• Et cetera ...

My advice borne of experience is that the bigger the project, the more "proper" techniques you need to use and the harder you need to push back on management who will pressure you for a quicker development cycle at the expense of proper development methodology.

So just do what you always knew you were supposed to do on the smaller projects, but never had time or management buy-in to do.

In terms of getting management buy-in, I would recommend doing your best to convince them that as a project grows in size, its complexity grows exponentially; thus, company will save money in the long run on any big project by investing in proper design and development practices up front and dramatically reducing maintenance and development costs in the long run. If they're unwilling to do that, I would question whether the project should be pursued in the first place. After all, if they balk at taking the time to do things right, they are implicitly telling you that they don't expect the project to be around very long.