A Close Date should never be in the past - The “Close Date” is your best estimate of when you expect to close the sale. This will change as you work the sale. It should never be set in stone as it affects your sales pipeline
Keep your opportunities up to date - An opportunity that has sat for a week or more without a firm follow up time set is most likely going to be lost. You should record at least one or more activities per week per opportunity, even if it is just an update email.
When using line item Products, be sure to utilize the Quotes feature. Send your customers Quotes with line items. This gives them something tangible to get their budget approved for the sale.
Update information about opportunities as they move through each gate of the sales cycle. By tracking the status of an opportunity through the sales cycle from creation to closure you and other team members will have a very good picture of where your deal is in the process.