How do I plan for a miles redemption with points accumulated for Krisflyer/Asia miles?

You need to know where you intend to travel first. Then calculate the miles needed. Look up for any sign up promotion for credit cards of banks you do not own, plan your expenditure so that you can eat the sign up promoiton criteria to get the miles.

You really need to plan your ependiture to optimis miles accumulation

If you have enough miles, you'll need to find award space first on the route you plan to fly. This can be tricky, so be flexible with your travel dates. Be flexible with your routing. This can make finding a suitable flight a lot easier.

Once you have found award space on a suitable date, just perform your redemption and get your flight ticketed and you will be good to go.

Alaska Miles can be useful if KF or Asia Miles don't have an option to fly to where you want to go. There are some sweet spots for that as well.