Are you sure? It's not good enough to feel like you know how to be anonymous on the Internet. To have good confidence you need to know why you remain anonymous. In other words you need to understand all the ways your anonymity might be compromised.

Mixing services don't necessarily unlink you from any coin trail. If, for example, you send properly mixed coins back to a wallet you control, which are mixed with other coins that might be linked back to you the mixing in the earlier step may be irrelevant.

No the chances are pretty good, because you often need to combine unspent outputs from multiple origins to reach a desired amount for a transaction.

The reason people say bitcoin is pseudo-anonymous is links back to identity are not obvious. However, that doesn't mean links are not there, and because transacting bitcoins on the blockchain is literally publicizing all transfer links, the smallest slip up anywhere going back to any point can be enough to establish a link to you.

There are two things which can alleviate that concern. The first is expecting low level of scrutiny of transactions. It's not worth it for an investigator to perform deep analysis on a bunch of data to find someone who committed some minor infraction, especially if the trail has been muddled by various obfuscation techniques, such as coin mixing. Alternatively one may expect a high level of scrutiny, but understand and practice, correctly and consistently, effective obfuscation techniques. The level to which that's necessary all depends on the activity.

Anonymity exists in a range from none or some to nearly perfect, but never perfect. Activity performed with coins therefore should fit the user's ability and practices when considering transaction scrutiny.

The government goes after the lowest hanging fruit. Keep your IP Address, shipping information, and obvious payment information (credit card => awful idea) away from any third parties and you're good to go. At the very least this means using a VPN/Tor/combination with a separate browser that won't supply tracking information. Watch those cookies and temporary files.

Less obvious information to keep away: Shared user names. Silk Road tag the same as your blog tag? That's how you get doxed. The government doesn't need probable cause to follow up on a lead.

Paying with Bitcoin through a mixing service is unlikely to do you in.

Mixing services don't necessarily unlink you from any coin trail. If, for example, you send properly mixed coins back to a wallet you control, which are mixed with other coins that might be linked back to you the mixing in the earlier step may be irrelevant.