Isn't social media great? It sure can be a great networking tool, but let's not forget about proper etiquettes. You worked hard to be seen, so when someone finally notices you, you don't want it to be for the wrong reason.
At the very least, customize your avatar, preferably with your photo. Nothing more dull than your tweets attached to a generic avatar. Make sure your photo looks presentable - meaning clear focused, lighting adjusted and half way professional looking.
2. Don't duplicate
This includes intentional and unintentional. Unintentional duplication could be caused by your plugin or social account linking. Are you auto-tweeting your blog? Updating from Facebook? Make sure you are not overlapping your connections somewhere between your accounts. There's also intentional repeating of your tweets, either literally or by changing the wording slightly. Once in a while may be a good promotion, but if every third tweet is the same stuff, it's too much.
3. Don't keep pitching
You want to sell, I get it. But instead of pitching the same line over and over, try offering some value and information that will be interesting to your target market. Once people see there's something to gain, it'll be much easier to sell them your products.
4. Come up with original stuff
Sure, retweets and quotes are great when you find something interesting, but produce your own content too. If all you tweet are borrowed texts, why should anybody follow you?
5. Quality vs. Quantity
I know you want maximum exposure, but massive quantity, especially with one or combination of the previous three items, won't be effective. Think about it, your followers are following many other people. Over-tweeting will make them numb. Don't clutter their tweets, and maybe they'll pay more attention when they see yours.
6. Respond accordingly
Use a Twitter client such as TweeDeck that lets you monitor keywords, and add a column for your name and your user name. You may not follow back everybody who follows you, but you want to know when someone @ replies, retweets, or mentions you so that you can properly respond back to them. If you are following many people, you may also want to add a column for direct messages. Be courteous.