Hey Tanya,

It depends on your qualification and knowledge:

If you are in 11th class then you should start with 

1 periodic table

2 chemical bonding

3 Stiochiomerty

If you are in target then you know better your level and start your preparation accordingly.

You can foucs on important chapter like

Solution 

Electrochemistry

Organic

Inorganic

Thermodynamics

Equillibrium.

Good Luck!