Dreamweaver's Clean Up HTML feature (accessed via Commands | Clean Up HTML) is no all-purpose HTML validator, but it does a pretty job at tidying some of the more obvious tag problems - especially removing redundant tags and combining nested FONTs.
   There are other housekeeping operations that aren't suited to the Clean Up HTML command (or the even more necessary Clean Up Word HTML). Fortunately some nifty footwork with the advanced features in Dreamweaver's search-and-replace function will often achieve the desired end.
   Say the original contains a number of CLASS attributes on the P tag, and you want to replace them all with a simple classless <p>. Go to Edit | Find and replace, and select Specific tag from the Find What list. Nominate the specific tag - p for paragraph. On the next line, leave the default With Attribute untouched and select class from the dropdown list. Leave the equals sign and select any value in the final box.
   Now for the replacement. In the Action list, select Replace Tag & Contents and enter the simple <p> tag in the Replace with area.
   Start the operation, and if it's useful it also makes sense to save the replacement query for reuse - click on the save-to-folder option.
   This is a simple example, but it is possible to set up very complex replacement parameters by adding more search layers with different settings that include or exclude other attributes within a tag. This isn't documented particularly well - there's more under the Help command than you'll find in the manual, as it happens - but it does repay experimentation.

If you need a quick and accurate tree-diagram site map, just click on Site and select the site you want from the list in the selector box. Now click the map icon (the tree-view button at the top left) to create a visual representation of your site. Now use File | Save Site Map to save the site map as an image file.
   The results probably won't be directly useable as a navigation tool for visitors - the site map will include entries for JavaScripts and mailto commands, for instance, and there may be too much literal-minded clutter. But it's handy for development purposes. And you could open the image in an image editor to edit it, then use Dreamweaver's inbuilt image mapping to set up clickable hotspots to take the visitor directly to a particular page on the site map (the map-drawing tools are on the Property Inspector panel) .

Dreamweaver is a large and complex development system, which means it will benefit greatly from the kind of speed tweaks that apply generally to the Windows environment - extra memory, big caches, defragging, the minimum number of fonts, and so on.
   You can also gain a few percentage points of improvement by keeping Dreamweaver itself as trim as possible. In particular, get into the habit of saving frequently. It's good practice, of course. But if you've been editing your Web page for a while and Dreamweaver is behaving a bit sluggishly, it's likely that your Undo stack has become quite large. Dreamweaver stores multiple Undos, recording all changes since the last save operation. If you haven't saved for a while, Dreamweaver will accumulate a lot of Undos in memory.
   While you're in the mood, minimise the size of the History panel. The History panel (Window | History) also tracks every edit you make, enabling you to undo or redo multiple steps with one click. At least you can limit the number of actions stored by using Edit | Preferences | General and setting the Maximum Number of History Steps (the higher the number, the more memory the History panel requires).