If you want to load modules from a path relative to where the script runs, such as from a "lib" subfolder", you need to use one of the following:
$PSScriptRoot
which works when invoked as a script, such as via the PowerShell command
$psISE.CurrentFile.FullPath
which works when you're running inside ISE
But if you're in neither, and just typing away within a PowerShell shell, you can use:
pwd.Path
You can could assign one of the three to a variable called $base
depending on the environment you're running under, like so:
$base=$(if ($psISE) {Split-Path -Path $psISE.CurrentFile.FullPath} else {$(if ($global:PSScriptRoot.Length -gt 0) {$global:PSScriptRoot} else {$global:pwd.Path})})
Then in your scripts, you can use it like so:
Import-Module $base\lib\someConstants.psm1
Import-Module $base\lib\myCoolPsModule1.psm1
#etc.