I am not a lawyer, of course, but here is my general advice:
Learn to write proactive e-mails describing your current state and giving concrete reasons with supporting evidence for your plans and requests. That is, consistently let management know what you need to perform your duties (training, tools, licenses, etc.) and provide some metrics or other evidence to justify it (for example, that you have not been trained on "X Product" that is critical to your enterprise, request some formal training, and list a few things that you are doing on your own to make up your gap such as purchasing and reading a book, manuals, joining an online group, etc.). Similarly, if you are about to make a major change that might involve some downtime, send a memo explaining what you are going to do and why (Because "X Server Version" is going out of support from its vendor, I am going to upgrade to "Version Y". I have requested a new server to do a migration rather than an upgrade per best-practices [cite source of best practices if necessary], but the requisition has been denied due to lack of funds. As I believe that the lack of vendor support is a major issue that must be addressed, I am therefore going to perform the upgrade on our existing hardware after performing a standard backup of our resources. I would like to schedule potential downtime for .... etc. etc.)
These are just examples, and you don't have to be quite that wordy or deferential. The important elements are that:
You let management know what you are doing and give them time to evaluate any decisions they may need to modify.
You provide reasoning for your decisions and requests that is backed up by some verifiable evidence. Especially when dealing with constrained resources (too few people, not enough budget) you need to explain your tradeoffs and prioritization without implying blame.
You always have a plan in place should problems occur and inform management of best and worse case scenarios.
You can demonstrate that you are proactively trying to improve your practices and skillset, and that you are acting positively on any direct guidance that you are being given from above. The purpose of these messages is not to shift decision-making in IT to others, but to provide a universal record of your decision-process, recommendations for future improvements, current activity, and skill set.
Above all, be honest and informative. Your copy of this correspondence will help you if you are in trouble, but hopefully through it you won't get into any trouble in the first place but rather be an asset to the company. The worst that happens when you do this is that you get a reputation for being overly verbose and cautious, but since the stereotype of the sysadmin is the opposite (the proverbial BOFH), it's better to be on this side.
You can ALWAYS be sued, since the bar for initiating a lawsuit is fairly low. But being successfully sued requires that they prove negligence on your part, and a long paper trail demonstrating your reasoning and informing management of your state will go a long way towards disproving it. Of course, it will also help in a positive way as you will gain a reputation as either someone who shares information and makes grounded decisions.