Cash runway is how long the money on hand lasts at the current rate of spending. It is a division: cash divided by monthly burn. Only three things move it.
Reduce what goes out each month
Lowering burn lengthens runway permanently rather than once, because it changes the divisor. A thousand saved every month is worth far more to runway than a thousand saved once.
The places this usually lives are overhead, software subscriptions, and operational waste. Cost that varies with the work is a different decision, because cutting it cuts revenue too — see fixed and variable costs.
Collect what is already owed sooner
Work already done and not yet paid for is the fastest source of cash, because the earning is finished and only the collecting remains. See money owed to you, collections and days to get paid.
This is a one-off gain. Once receivables are current the well is dry, and what remains is the ongoing improvement of collecting faster than before.
Bring in money that is not sales
A credit line, an owner contribution, a loan, or an equipment sale. This buys time without changing the underlying rate, so it extends runway without improving the business.
Borrowing also adds a repayment, which raises burn from the following month — see debt service coverage.
The timescales differ
Collecting receivables works in weeks. Cutting cost works from the next billing cycle. Winning more profitable work works in months, which is why it is not a response to a short runway even though it is the only permanent fix.
A runway short enough to be alarming is answered with the first two. The third is what stops it recurring.