How to desing Good theme in magento

how we can design good theme in magento? first of all we have to decide what type theme we are needed.

what step we have to follow.
1) First of all we have to look about theme brand and logo.
2) how many products and categories we have to use in our theme, store.
3) what type of products we want to sell
4) In what country our website will be published.
5) What languages we will use in our website.
6) how many slider and brand we are using in our theme.
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we need follow more things for better designing...i will post soon more meter

Show all sub categories with thumbnail

create file in location: aa/desing/frontend/ theme/catelog/category/subcat.phtml
<?php
$category = Mage::getSingleton('catalog/layer')->getCurrentCategory();
$categories = $category->getCollection()
        ->addAttributeToSelect(array('name', 'thumbnail'))
        ->addAttributeToFilter('is_active', 1)
        ->addIdFilter($category->getChildren())
?>
<ul class="subcategories">
    <?php foreach ($categories as $category): ?>
        <li>
            <a href="<?php echo $category->getUrl() ?>"><img src="<?php echo Mage::getBaseUrl('media')?>catalog/category/<?php echo $category->getThumbnail() ?>" height="150" width="150" alt="<?php echo $this->htmlEscape($category->getName()) ?>" />
                <span><?php echo $category->getName() ?></span></a>
        </li>
    <?php endforeach; ?>
</ul>

how to call in:
{{block type="core/template" template="catalog/category/subcat.phtml"}}

create static block and past code: {{block type="core/template" template="catalog/category/subcat.phtml"}}

Now go to admin, select particualr category and click to display setting tab and select Display Mode "  static block only "  and select CMS Block...

ENJOY :)