How to do performance improvement in an existing code

Hi Team,

I need to tune the performance of an existing interface which has around 2 k lines of code.

The performance lags during the stages of ,

        1) Page Load - Taking more time with "Working..." message. 

        2) Drop Down Selection - Taking more time to display, when we select any drop down boxes., with "Working..." message.

I have checked the DB objects and all looks good from the DB tuning perspective.

What would be your approaches for performance tuning ? Please help me with some tips.

Below is a sample template for which am looking for a performance improvement.

Sample Code Structure:

= load (
local!a: rule!a(cons!a),
local!b: rule!a(cons!b),
local!c: rule!a(cons!c),
local!d: rule!a(cons!d),
local!e: rule!a(cons!e),
local!f: rule!a(cons!f),
local!g: rule!a(cons!g),
local!h: rule!a(cons!h),
local!i: rule!a(cons!i),
local!j,
local!k,

a!formLayout(
contents:{
rule!abcd(
....
....
....
),
with (

.........

/* Dynamic Section Layouts based on conditions */
.........
.........
.........
),
with (

.........
/* Multiple Section Layout based on conditions */
.........
.........
.........
),
a!buttonLayout(
.........
.........
.........
)
}
)

)