Define stages by what the customer has done rather than by how you feel about it. Enquired, spoke to me, received a proposal, agreed, are all observable events. Interested, warm, and likely are opinions, and a pipeline built from opinions tells you nothing you did not already believe. The test for a well defined stage is whether two people looking at the same opportunity would place it identically.
Keep the number of stages small. Four or five covers almost every small business, and each additional stage is another thing to maintain for information you will not use. What you want to see at a glance is how many opportunities exist, where they are stuck, and which ones have had no contact recently.
That last point is the actual value. The pipeline earns its place by surfacing the opportunity that has sat at proposal sent for three weeks while you assumed it was progressing. Every entry needs a next action and a date, and reviewing the list weekly for anything without one takes ten minutes and recovers work you were unknowingly abandoning.
Include a closed and lost stage and record the reason. After twenty entries, the pattern in why people did not proceed is more useful than anything in the won column, and it is usually not the reason you would have guessed.
Resist the temptation to attach a probability percentage to each stage, which is a habit borrowed from larger sales organisations and produces false precision at small volume. With ten opportunities, weighted forecasting is arithmetic performed on guesses. What you actually need is the count at each stage and the age of each entry, because those are observable. Revenue forecasting from a small pipeline is unreliable regardless of the method, and treating it as reliable is how businesses commit to spending against work that does not close.
Review it at a fixed time each week rather than when something occurs to you, because the value is entirely in catching the opportunity that has gone quiet. Fifteen minutes scanning for anything without a next action, or with a date that has passed, recovers work you were unknowingly abandoning and it is the single habit that makes the pipeline worth maintaining.