Improve instructions

generator/generate.html

                 </div>
                 <div class="modal-body">
                     <ul>
-                        <li>The generated cards open in a new tab or window. If you don't see any new tab or window, check your popup blocker.</li>
-                        <li>Make sure to use the correct paper size (same as in the editor).</li>
+                        <li>The generated cards open in a new tab or window. If you don't see any new tab or window, check your popup and script blockers. If that does not help, try disabling all addons.</li>
+                        <li>Make sure your printer uses the correct paper size (same as in the editor).</li>
                         <li>Enable double sided printing (flip on long edge).</li>
-                        <li>Do not scale the document to fit the page.</li>
+                        <li>Do not scale the document to fit the page. Print at original size.</li>
                         <li>
                             Some printers are not very precise (pages print slightly shifted or rotated) and the cards will not line up with the card backs.
-                            If this is the case, there's nothing you can do. Try a different printer or print single-sided.
+                            If this is the case, there's not much you can do.
+                            Try making the page background the same color as the cards, so that you won't get any white edges on the card.
+                            If that does not help, try a different printer or print single-sided.
                         </li>
                     </ul>
                 </div>

generator/js/ui.js

 
 var ui_generate_modal_shown = false;
 function ui_generate() {
+    if (card_data.length == 0) {
+        alert("Your deck is empty. Please define some cards first, or load the sample deck.");
+        return;
+    }
+
     // Generate output HTML
     var card_html = card_pages_generate_html(card_data, card_options);