If you want more volume on the dex you need to get the web client running fast and smooth. Right now it is very slow to low on normal low bandwidth connections. Often it wont load the wallet balance or orderbook on slow connections making the dex dead to folks using the web client. High speed performance is crucial for the web client to get more volume
And just to add regarding their Waves DEX. They should also focus on making the platform more appealing to the eye of its customers. I don't know about other people but the aesthetics of their platform is somehow a "meh" to me. Add that to the sluggishness of the site and people will definitely stay away from their DEX and will just check other exchange that provide quality service to its traders.
And I have to agree with you about their orderbook. It is very confusing and take note, I'm not a newbie trader so I know how to navigate different trading platforms but man, I don't think the person who designed it even traded cryptocurrencies from other website/exchange.