xWhen it comes to web hosting, it's important to consider two things: where you will host your domain, and where you will host your site. Domain registrars are very important because if you pick an untrustworthy one you may lose an irreplacable domain name, web hosts are important because without them your site is offline and inaccessible - thus, both your service providers must be stable, reliable companies.
For web hosting services, your best practices is to get to know the web host - in fact, having a friend "inside" the company is the single best way to ensure you're treated fairly and get the best service. While, it may not mean anything for reliability and network quality, it will mean a lot in terms of support and services offered.
Email the web host, ask them questions, particularly really specific questions (even if you know the answers already), email both the sales@ email address, and the support@ address. Remember, sales email addresses are usually much more active in terms of response time than support addresses, it's important to check both, since the support address will be the one you'll end up dealing with.
Learn about "pinging" servers to test their response speed, compare web hosts speeds, etc. In your email to the support staff, ask what the average load and memory use on their shared servers is. If it's too high, stay away.
Check out some of the major web hosting related communities - WebHostingTalk.com is the biggest and easily provides the most discussion of shared, reseller and dedicated hosting providers, allowing you to find the best deals, make some web hosting-related friends and just generally make sure you don't get ripped off.
For domain registrars, usually the cheapest is the best - since truly, the services they offer aren't all that important. though, reliability is. There have been some shady registrars who have been known for stealing domain names from clients, locking their accounts, etc. Sticking with the big names: NameCheap, GoDaddy, Register, etc. will keep you out of trouble.