What are The most important Basics That should be considered when starting An Interior Lighting Design ?

when you are stating designing the interior lights of any building first you should study the functions of all places and areas and the material you are using , 2nd the furnture depending on the functions of the places .

Thank you for your invitation, and sorry for my late reply.
Main basics to start your lighting design is:
1- Determine the purposes for using light in the space, just to make people see or to contribute to the mood of the room.

2- Be aware of your room direction and exposure, this's important to know the amount and intensity of your daylight , and how it could be included in your lighting design.

3- Decide which type of artificial lights you are going to use: Ambient, Task lighting, or Accent Lighting.
Each has it's purpose and amount of light.
This depends on the function of your space.

4- Decide the colors: a- Color of your light, yellow or white.
This choice affects colors in your room.
b- Color of your lighting fixtures, they also contribute color to a room A basic understanding of how light influences color can help you make wise color and lighting choices.

5- Finally,this is an additional step but preferable to start or finish with, visit some lighting showrooms, a new lighting fixture can give you some new ideas.
Note: It would help a non-specialist designer to have some advises from a good electrical technician.

Great answer from Sherein Sorour, I learnt a lot.
Thanks

First what's the space is used for : relaxing, studying..etc so you can determine the light type second where is your center objects and last the colors and materials because light color and type can enhance or mess furniture color!

http://www.iar.unicamp.br/lab/luz/ld/Arquitetural/Handbooks/Lighting%20Design%20Basics.pdf

Download the PDF and study

1- understand the function of the area you are going to light.
2- paint colour and furniture colour and shape are very important to be known.
3- to know the different kinds of lamps ( lighting)
4- to syudy power consumption of these lamps.

Sherein Sorour  provided the most detailed answer one can probably ask for but to further expand on her first point, Lux requirements of the space is a Must and should be checked against CIBSE regulations or any local codes u might have. The required lux level can give u the idea of minimum lumens for the space and out of that u can figure out the number of lamps required to achieve that lux level.