$data = array('param1' => $items, 'param1' => $location, ....); // Plugin parammeters
JPluginHelper::importPlugin('myplugins', 'plugin_name'); // Load plugin

$dispatcher = JDispatcher::getInstance();

$result = $dispatcher->trigger('getMyFunction', $data);

$this->items = $result[0];

$option = JRequest::getVar('option'); // Get component name
$app = JFactory::getApplication();
$params =& JComponentHelper::getParams($option);

$mode = $this->params->def('mode', 1);

$plugin = JPluginHelper::getPlugin('user', 'userdirect');
$pParams = new JRegistry();
$pParams->loadJSON($plugin->params);
$link = $pParams->get('group_1');

OR 

$plugin =& JPluginHelper::getPlugin($plgType, $plgName);
$params_object = new JParameter( $plugin->params );
// to get 1 parameter from a plugin
$param_item = $params_object->get('name_of_param');

$componentParams = &JComponentHelper::getParams('com_example');
$param = $componentParams->get('parameter_name', 'default_value');

$componentParams = &JComponentHelper::getParams('com_example');
$param = $componentParams->get('parameter_name', 'default_value');

$param = $params->get('parameter_name', 'default_value');

$module = &JModuleHelper::getModule('module_example');
$moduleParams = new JParameter($module->params);
$param = $moduleParams->get('parameter_name', 'default_value');

$param = $this->params->get('parameter_name', 'default_value');

$plugin = &JPluginHelper::getPlugin('plugin_example');
$pluginParams = new JParameter($plugin->params);
$param = $pluginParams->get('parameter_name', 'default_value');

$param = $this->params->get('parameter_name');

jimport('joomla.filesystem.file');
$mainframe = &JFactory::getApplication();
$params = $mainframe->getParams(JFile::read(JURI::root().'/templates/template_name/params.ini'));
$param = $params->get('parameter_name', 'default_value');

$paramsFile = dirname(__FILE__) . '/../params.ini'; // Get params.ini

// check if file exists
if(file_exists($paramsFile)) {
    $iniString = file_get_contents($paramsFile); // get ini file contents
    // Escape double quotes in values and then double-quote all values
    $iniQuoted = preg_replace('/=(.*)\\n/', "=\"$1\"\n", addcslashes($iniString, '"'));
    $iniParsed = parse_ini_string($iniQuoted);
} else {
    $iniParsed = '';
}
$params = (!empty($iniParsed)) ? $iniParsed : array();
$param = $params['paramName'];

$Plugin =& JPluginHelper::getPlugin('system', 'saleslogix');
$dispatcher =& JDispatcher::getInstance();
$plg = array("type"=>"system","name"=>"saleslogix","params"=>$Plugin->params);                  
$saleslogixPlg = new plgSystemSaleslogix( $dispatcher, $plg );
//$resultHere = $saleslogixPlg->myFunction();

JPluginHelper::importPlugin('system');
$app = &JFactory::getApplication();
$app->triggerEvent('onAfterInitialise');

<?php
function CreateNewUser($name, $username, $email, $password, $registerDate = NULL, $usertype = 'Registered', $block = '0', $sendEmail = '1', $gid = '18') {
        global $db;

        $db = & JFactory::getDBO();
        jimport('joomla.user.helper');

        //Make the joomla password hash
        $salt = JUserHelper::genRandomPassword(32);
        $crypt = JUserHelper::getCryptedPassword($password, $salt);
        $joomlapassword = $crypt . ':' . $salt;

        //Table #__users
        //Informations about the user
        $user = new stdClass;
        $user->id = NULL;
        $user->name = $name;
        $user->username = $username;
        $user->email = $email;
        $user->password = $joomlapassword;
        $user->registerDate = registerDate;
        $user->usertype = $usertype;
        $user->block = $block;
        $user->sendEmail = $sendEmail;
        $user->gid = $gid;

        if (!$db->insertObject('#__users', $user, 'id')) {
            echo $db->stderr();
            return false;
        }


        //Table #__core_acl_aro
        //Discover what is the last value of value in #__core_acl_aro
        $query = "SELECT value FROM #__core_acl_aro ORDER BY id DESC LIMIT 1";
        $db->setQuery($query);
        $coreaclarolastvalue = $db->loadResult();

        $coreaclaro = new stdClass;
        $coreaclaro->id = NULL;
        $coreaclaro->section_value = 'users';
        $coreaclaro->value = $coreaclarolastvalue + 1;
        $coreaclaro->order_value = NULL;
        $coreaclaro->name = $name;
        $coreaclaro->hidden = NULL;

        if (!$db->insertObject('#__core_acl_aro', $coreaclaro, 'id')) {
            echo $db->stderr();
            return false;
        }

        //Table #__core_acl_groups_aro_map
        $coreaclmap = new stdClass;
        $coreaclmap->group_id = $gid;
        $coreaclmap->section_value = NULL;
        $coreaclmap->aro_id = $coreaclaro->id; // maybe just $user->id ?

        if (!$db->insertObject('#__core_acl_groups_aro_map', $coreaclmap)) {
            echo $db->stderr();
            return false;
        }

        $CreateNewUserInfo = array($user->id, $user->name, $user->username, $user->email);
        return $CreateNewUserInfo;
}

//This exemple will take data from one post, for example
$username = JRequest::getVar('username');
$name = JRequest::getvar('name');
$email = JRequest::getVar('email');
$password = JRequest::getVar('password');

//This code will call your funcion, then register with your data
$NewUserInfo = CreateNewUser($name, $username, $email, $password, $registerDate);

<?xml version="1.0" encoding="utf-8"?>
<install version="1.5" type="plugin" group="system">
	<name>System - Name of Plugin</name>
	<author>Name of  author</author>
	<creationDate>19th April 2010</creationDate>
	<authorEmail>
 This e-mail address is being protected from spambots. You need JavaScript enabled to view it
 </authorEmail>
	<authorUrl>http://www.khawaib.co.uk</authorUrl>
	<version>1.0</version>
        <copyright>Copyright (c) 2010 Khawaib Ahmed. All rights reserved.</copyright>
	<license>http://www.gnu.org/copyleft/gpl.html GNU/GPL</license>
	<description> Plugin description.</description>
	<files>
		<filename plugin="phpFileName">phpFileName.php</filename>
	</files>
	<params>
		<param name="code" type="text" default="[DEFAULT VALUE]" label="[LABEL]" description=" [DESCRIPTION]"  />
	</params>
</install>

<?php
// no direct access
defined( '_JEXEC' ) or die( 'Restricted access' );

jimport( 'joomla.plugin.plugin');

class plgSystemAsynGoogleAnalytics extends JPlugin {
	function plgAsynGoogleAnalytics(&$subject, $config) 	{
		parent::__construct($subject, $config);
		$this->_plugin = JPluginHelper::getPlugin( 'system', 'AsynGoogleAnalytics' );
		$this->_params = new JParameter( $this->_plugin->params );
	}
	
	function onAfterRender() {
		global $mainframe;
		
		// skip if admin page 
		if($mainframe->isAdmin()) {
			return;
		}

		// get params
		$trackerCode = $this->params->get( 'code', '' );
		
		//getting body code and storing as buffer
		$buffer = JResponse::getBody();
		
		//embed Google Analytics code
		$javascript = "<script type=\"text/javascript\">
					  var _gaq = _gaq || [];
					  
					  _gaq.push(['_setAccount', '".$trackerCode."']);
						_gaq.push(['_trackPageview']);
					
					  (function() {
						var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
						ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
						var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
					  })();
					</script>";

		// adding the Google Analytics code in the header before the ending </head> tag and then replacing the buffer
		$buffer = preg_replace ("/<\/head>/", "\n\n".$javascript."\n\n</head>", $buffer); 
		
		//output the buffer
		JResponse::setBody($buffer);
		
		return true;
	}
}
?>