Alt is good. They are only the names of the t-shirts and without accompanying text beneath it serve its purpose.
General Tips for Increasing Conversion Rates:
Mostly is focussed around the shopping cart. Making sure questions are answered quickly like; shipping costs, returns, contact info, phone number, where do you ship to etc.
If you have a telephone number put it on every page a good place is at the top. A 0800 number is good.
Make the shipping costs obvious without having to checkout. Links from the cart help, ones that don't take them away from the cart are better - doesn't lower the conversion rate that way. "Free shipping" is an obvious increase in conversion, add that to pages if you can offer that.
Return policy. Make this quickly identifiable in the cart and else where on the site.
Make it evident that the cart checkout process is secure. SSL.
Limited steps in the checkout process. 3 steps are good, fewer better.
Don't make the customer have to sign up to checkout. Always allow checkout without having to sign up, if you have that option. Also don't make that an extra step in the process. Put it on the same page as the checkout.
Believe it or not, colours, placement of text, positioning of buttons can all affect conversion. Just playing with these and analysing the changes can have an affect on conversion. Action buttons are much needed in a cart. Make them obvious as the next step. buttongenerator.com is awesome for this.
Put anchors on your Order FAQ page and make separate links to the content. e.g.
information.php?info_id=5#returnpolicy
information.php?info_id=5#shippingcost
Then add those separate links to your cart. Return Policy | Shipping
"We ship worldwide" is also good.
Make the customer aware that the product is "In Stock" in the cart and let them know when it will ship.
That's a few tips. You seem to have the information there you just need to make the links and that will definitely up your conversion rates.
Another thing, knowledge is power. Make sure you know what people are looking at on your site, where they go, when they leave. Keep an eye on how many people add things to cart and checkout. That is how you will see if your conversion rate goes up or down. Good session tracking software is needed for this.
P.S. Your site is awesome
