What does eclectic mean? Looking at a dictionary, we see...
1. Selecting or choosing from various sources.
2. Made up of what is selected from different sources.
3. Not following any one system, as of philosophy, medicine, etc., but selecting and using what are considered the best elements of all systems.
Really, that's about all there is to it. Spiritually speaking, to be eclectic means to pull what works for you from various sources, to put those different elements together into a working path. Although I usually just call myself a hedgewitch, it would be accurate to say I'm an eclectic hedgewitch. There are hedgewitches who work only with the symbols, belief, deities, etc. of one culture - but many of us, myself included, usually find ourselves pulling from a few different cultures, for multiple reasons.
Some people take a bad view of eclectics - we can be seen as flippant, indecisive, lazy, disrespectful. Truthfully, there are certainly some eclectics who fit that description, but there are many more who don't.
If you're going to be eclectic, it does take work. Being an eclectic should not just be about doing "whatever you want," it needs to be about doing what actually works for you, and those are not always the same thing. Beyond, that is it also not always about doing what "feels good" or "feels right." To grow spiritually we must know our personal limits, and occasionally push past them. Spiritual growth is not always good feeling, it can be uncomfortable or downright painful, but that is necessary at times.
So how do you find what works? The first step is often study, and lots of it. Know the original context of the idea/practice, know the history behind it, know why it was done, how, the real meaning of it. Occasionally some of that knowledge may be lost to history, but we should learn what we can. If we're talking about a Deity, same thing, study their history, their mythology, how they were traditionally worshiped, and so on. You don't have to worship a deity exactly as was done historically, but it's good to know the information, and it can keep you from doing something that would be seen as inappropriate.
After studying, an idea can be put into practice. Try it out. Experiment a bit. If it works well for you, you can work on incorporating it into your personal practice. If it doesn't? You may want to give it a few more tries, but if it still isn't working after a good while, you can move on to find something that does. You don't have to force yourself into doing something that just isn't working, but some techniques may require persistence to really get right.
Being eclectic is not about just grabbing anything pleasing and shoving it all together, hoping that you get something somewhat functioning. We need to be respectful to the cultures we borrow from - and sometimes, that can even mean not borrowing a particular practice or belief at all.
Remember, these are often sacred symbols, beliefs, and so on - not just to the original culture, but if you're going to incorporate it into your practice then they are sacred to you too. Treat them that way.