Free Spins
It is best to use free spins when when they are the most expensive (i.e. round 19 or 20).
When to use free spins:
One spin
round 20
Two spins
rounds 19 and 20
Three spins
rounds 18, 19 and 20
Exception: If you have one or two numbers left, you might want to use your free spins earlier. Generally, unless I have 1 number left, I use my free spins when the rounds cost the most.
Where to place jokers.
This is especially important for columns 2 and 4. Placing a joker can result in one, two, or three complete lines. Obviously you want to complete as many lines as possible.
In order of preference, place your jokers as follows:
3
3
2
2
1
2
2
3
3
Look before you leap! Don't just click on the first empty square when you have a joker. Look at the other numbers you received. You might realize that putting it somewhere else will complete a line.