Sure, its good enough. If you want to adjust any setting, just wait. Give Avast! a little time on your system. How much? Depends on how much you use the pc per day/week. But generally, get used to the default settings. That way if you adjust a setting, and in short order something goes awry, you know the changed setting is most likely the culprit.

Now, once you get used to defaults, there are setting that are relatively safe to change (i.e. turning up heuristics on the Web Shield), and others that can really lead to trouble (like “scan all files” on the File System Shield). Any question about any specific settings change, feel free to ask.

edit: Good second opinion scanners that wont conflict with Avast!
http://www.superantispyware.com/ (the free one)
http://www.malwarebytes.org/products/malwarebytes_free