Applying eyelash extensions is a delicate and intricate process that requires skill, patience, and attention to detail. Here's a general overview of the steps involved:

1. Prepare the client: Start by cleansing the client's eyelashes and removing any makeup or oil. Then, have them lie down on a comfortable surface with their eyes closed.

2. Select the appropriate lashes: Choose the right type and length of lashes based on the client's natural lash type, desired look, and personal preference.

3. Apply under-eye pads: Place under-eye pads on the client's lower lashes to prevent glue from getting on them.

4. Prepare the lashes: Isolate a single natural lash and apply a small amount of lash primer to help the extensions adhere better. Then, pick up an extension with tweezers and dip the base into a small amount of glue.

5. Apply the lashes: Carefully attach the extension to the natural lash, making sure not to touch the eyelid or other lashes. Repeat the process for each natural lash, working in a zig-zag pattern across the lash line.

6. Allow the glue to dry: Let the glue dry for a few seconds before moving on to the next lash.

7. Repeat the process: Continue applying lashes until the desired look is achieved. Typically, a full set of lash extensions can take 1-2 hours to complete.

8. Finish and clean up: Once all the lashes are applied, gently brush through them with a clean mascara wand to separate and shape them. Then, remove the under-eye pads and clean any remaining glue or primer from the lashes.

It's important to note that applying eyelash extensions should only be done by a licensed, trained and certified lash technician to ensure safety and optimal results.