Option Explicit
Private Declare Function SetPriorityClass _
Lib "kernel32" (ByVal hProcess As Long, _
ByVal dwPriorityClass As Long) As Long
Private Const REALTIME_PRIORITY_CLASS = &H100
Private Const HIGH_PRIORITY_CLASS = &H80
Private Const NORMAL_PRIORITY_CLASS = &H20
Private Const IDLE_PRIORITY_CLASS = &H40
Private Declare Function OpenProcess _
Lib "kernel32" (ByVal dwDesiredAccess As Long, _
ByVal bInheritHandle As Long, ByVal dwProcessId As Long) As Long
Private Const PROCESS_QUERY_INFORMATION = &H400
Private Declare Function GetCurrentProcessId Lib "kernel32" () As Long

Private Sub SetPriority(Priority As Long)
Dim ProcId As Long 'переменная для id процесса
Dim ProcHandle As Long 'переменная для handle процесса
ProcId = GetCurrentProcessId 'получим id
ProcHandle = OpenProcess(PROCESS_QUERY_INFORMATION, False, ProcId)
'получили Handle
Call SetPriorityClass(ProcHandle, Priority) ' ставим приоритет
End Sub

Private Sub Form_Load()
'ставим приоритет
SetPriority HIGH_PRIORITY_CLASS
End Sub