Use variables instead of constants

If you are using given constant many times in your code, then why don't you store it in a variable and use the variable later. See the following two extracts of code. The second one executes faster.

'Ex.1

For X = 1 to 10000
A = X * 3.1415927
Next X

'Ex.2

PI = 3.1415927
For X = 1 to 10000
A = X * PI
Next X

Use simpler math operations

Different types of calculation take different time for the computer to process. Thus wherever you can, replace expressions like X * 2 with X + X, A / 10 with A * 0.1 or A^2 with A * A. They really run faster.

Be careful with repeating operations

Sometimes, a certain calculation may be done several times in vain. This could happen in many different ways. I will illustrate it with two simple examples.

'Ex. 1

For X = 1 to 1000
For Y = 1 to 100
P = X * 10 + Y
Next Y
Next X

'Ex.2

For X = 1 to 1000
T = X * 10
For Y = 1 to 100
P = T + Y
Next Y
Next X

The second example runs better, because X * 10 is repeated only 1000 times compared to 100000 times in the first one.

Use loops properly

Just take a look at the following to examples and you'll understand what I mean.

'Ex.1

For X = 1 to 10000
For Y = 1 to 10
P = X + Y
Next Y
Next X

'Ex.2

For Y = 1 to 10
For X = 1 to 10000
P = X + Y
Next X
Next Y

Count the times each line is executed and the results are simple:
 

Line No	Times in Ex. 1	Times in Ex. 2
1	1	1
2	10000	10
3	100000	100000
4	100000	100000
5	10000	10
All	120001	100001

Load most used forms in memory

Loading a form may cost a lot of time in heavy situations. Thus, you should load your most used forms when your application is not busy doing other things. A good idea is using a splash screen and loading your forms when your program is started. You can also do it when your program is being minimized, or has lost focus.

API vs. VB

In some cases, using API may be faster than calling VB functions. For example, retrieving a directory structure using API is about four or five times faster than using the standard VB functions. When working with graphics, you cannot miss to call an API. But not all the VBs are slow. You must experiment to find what does better. Just save Timer in a variable, make a loop calling a VB function and at the end display the time elapsed. Do the same with the API and make up your mind what will be worthy.

Big variables - ByRef rather than ByVal

When a variable is passed to a procedure ByVal, this mean it won't and cannot be changed by this procedure. If the procedure changes this variable, it does it for itself only, the original value is never affected. And here is how VB makes it - It just copies the variable to a new location in memory and gives this location to the procedure. But everyone knows that copying memory takes time. Now lets see what happens when a variable is passed ByRef. It's very simple, if the variable can be changed by the procedure, then it is not necessary that the procedure will be given a copy of this variable. VB just gives the procedure the original location of the variable. It just saves the time for creating a copy of this variable. So, when using big variables (mostly user-defined) pass them ByRef to safe some precious time.

Procedure calls loses time

It's true. When calling procedure or function a bit of time is wasted. It's just a little bit, but if your procedure consists of several lines and in your app code you call it 5000 time in a loop or something, then you should just copy this several lines in the loop to avoid losing much time. Your program may lose some readability, but it will gain speed.