If you really need to, you can convert some of your Functions into Gosub routines.  Functions require a small amount of overhead.   They have to push their called parameters onto a stack and pop them off when they return.  Gosubs don't require as much overhead and therefore can give you a speed advantage.

;use a Function (slower)
start = MilliSecs()
For n = 0 To 100000000
	myfunc()
Next
Print MilliSecs() - start

;use a Gosub (faster)
start = MilliSecs()
For n = 0 To 100000000
	Gosub mylabel
Next
Print MilliSecs() - start

WaitKey
End

Function myfunc()
	a=a+1
End Function

.mylabel
	a=a+1
Return

Goto is FAST.  It's the quickest way to get from one point in your program to another.   Sometimes, if you really need it, you can shave off a little time, by UNstructuring your code, and using a Goto to instantly skip from point A to point B.

The example provided isn't the best but does the job of showing how useful Goto can be.  In the example, the variables c, d, e, f, and g are only incremented if dontDoIt is False.  dontDoIt never equals False in this example so the variables are never incremented, BUT the computer still has to execute each If statement associated with each variable (If Not dontDoIt Then ...) as it exits each nested If a <> True statement.

In the second timed loop however,  the program uses the Goto to just jump immediately out of all of the nested Ifs at once (since there really is no reason to bother checking any of the c, d, e, f, or g variables) and saves some processing time.

Many programmers will tell you that using Goto is bad programming practice and produces 'spaghetti' code.  This can be very true but if you really need to tweak a certain section of your code, and you've tried other optimizations but you still need more, then this might be a solution that works, especially when you need to jump out of a number of nested Ifs.

start = MilliSecs()
For n = 0 To 100000000
	dontDoIt = False
	If a <> True
		If a <> True
			If a <> True
				If a <> True
					If a <> True
						If a<>True Then dontDoIt=True
						If Not dontDoIt Then c = c +1
					EndIf
					If Not dontDoIt Then d = d + 1
				EndIf
				If Not dontDoIt Then e = e + 1
			EndIf
			If Not dontDoIt Then f = f + 1
		EndIf
		If Not dontDoIt Then g = g + 1
	EndIf
Next
Print MilliSecs() - start

start = MilliSecs()
For n = 0 To 100000000
	If a <> True
		If a <> True
			If a <> True
				If a <> True
					If a <> True
						If a <> True Then Goto label
						c = c + 1
					EndIf
					d = d + 1
				EndIf
				e = e + 1
			EndIf
			f = f + 1
		EndIf
		g = g + 1
	EndIf
	.label
Next
Print MilliSecs() - start

WaitKey