CEO ask CFO: I need you to cut our operation cost this year by 10%. Where should you start?

Firstly i will ask his hidden agenda why we need to cut cost. If cutting cost is to increase net profit, i will suggest the following:
1) increase the top line
- expand new market/new clients
- widen product portfolio to the existing
2) Improve gross profit margin
- enhance production capability (more productivity)
- Re-Negotiate the material price (this option IKEA always does)
- sourcing new material suppliers with the same quality like the previous suppliers
- Carry out KAZEN, process improvement to reduce the defect rate,
- Focus on high margin product
3)Operation expenses
- benchmark the company rations vs peers (turnover/sales rep; sales cost/sales rep, per unit…) then have action plan for that
- Reduce above the line ad by below the line; frequency of ad
- regarding G&A:
+ cut extravagant expenses
+ implement energy efficiency to save energy and utility cost
+ Motivate to retain people to save recruitment cost
4) Financial expenses
-Control the cash flow (review distribution policy, credit) to decrease the borrowing amount to save interest expense

The first think i will do is consulting accounting department of company expenses analysis. Later holding a meeting with all company team leaders to get their idea about that. Finally, make my own decision about cost control base on what I get from the meeting.

If you are the CFO/or Business Leaders! You will be prepared and come up with the CEO a well-proportioned action plan for the fiscal year of course almost everything is done relatively, so any cost is reasonable.

According to your question I think priority in this case is the CFO must be cutting administrative costs as transaction costs (such as: receiving guests/visitors, clients, partners, controlled and avoiding to any bribery or corruption), office or bureau costs

Other divisions is followed

You should apply Business Risk Management. You determine the factors which influence on your business and how they do. After that you find out solutions and make a detail plan to act. Remember "increasing revenue is also way to cut cost"

There are 3 kinds of CEO approach to cutting costs:
- the growth leader CEO, he will ask Chief Marketing Officer to reduce the costs so that they dont make the mistake of cutting the R&D of next IPOD/IPAD department. Because that CEO vision the next income stream that will pay for the costs hugely
- the manager CEO, he will ask CFO to rationalize costs they will cut at the risk of demotivating staff (leaving ) or worse cut in the next Nintendo WII project under development. It will be very effective because he has done that all his life... then what is next? with no growth cut every one salary?
- the paternal CEO, he will ask Chief HR to gather all staff and explain that the savings is not a CMO/CHR/CFO job, it is every one saving from turning of light to seeing un-necessary expenses or cost cutting new procedures to contribute to save much more than -10% over the many years to come.
Chose who is the CEO you are?