What kind of plays could I make to convince my opponents that I have a polarised hand range?
You don't make plays to convince your opponents that you have a polarized hand range, you just polarize your hand range. If they fail to pick up on that, you've profited greatly.
There are generally three types of ranges:
Polarized
With a polarized range, your hand only contains strong hands and air (bluffs). This is an ideal range to have in most spots. Playing against an aggressive opponent who has a polarized range can be quite difficult at times.
Merged
With a merged range, you have strong, medium strength, weak, and air hands in your range. Basically, linear distribution of hands — you have something of everything.
Capped
With a capped range, you have no strong hands. You only have bluffcatchers/air. Your range is extremely weak.
You value greatly when an opponent doesn't realize you've polarized your range to include only strong value and air since you've obviously greatly increased your expectation with said air hands (your bluffs). As such, it's entirely counter-productive to try and convince opponents you have a polarized hand range.
What actions could I use to make it harder for my opponents to figure out what I'm calling, raising or folding with?
Ah, now we're getting into the territory of balance and game theory optimal play. This has been quite a hot topic for some years now.
When playing against recreationals, all you really have to think about is maximally exploiting your opponent so that you can maximize your profits. But if you are playing against a skilled, thinking opponent that is trying to do the exact same thing you are, things get far more complicated.
It becomes paramount to balance your strategies so that they aren't easily exploitable.
Take, for instance, the following situation that frequently occurs in heads-up hyper-turbo SNGs. Most regs will open 90%+ of all hands on the button. When playing other regs, they will frequently exploit this by 3-bet shoving a wide range of hands. But how do they choose said hands?
The math works out that, if an opponent is opening his button to 2x the blind with 70%+ of all hands, and is only calling with a tight value range {44+, A7s+, A8o+, KQs}, you can basically jam any two cards when he does so.

But, remember, we're playing a reg. We don't want to implement a strategy that is so obviously exploitable against a thinking opponent. And, on top of that, we are trying to maximize our expectation with each hand in our range. As such, we shouldn't be 3-bet shoving a hand like JTs as it will obviously have a better expectation by flatting his open than it will by 3-bet shoving it. Therefore, we polarize our 3-bet shoving range.

Now we're 3-bet shoving with our value hands as well as weaker suited hands that don't necessarily play well postflop (including weaker suited connectors is debatable here, it can go either way really). We've increased the expectation of weaker hands like J4s immensely by doing so, are exploiting the reg Villian's strategy quite well, and still have a good flatting range which consists of middling/strong hands that will flop well. Our strategy is hard to exploit unless the reg is paying attention and knows the appropriate adjustments (which, surprisingly, isn't the case a lot of the time).
The main point here is that of information hiding. Each time you have to make a decision, there will be multiple actions you can take. Check, call, raise, check/raise, check/fold, check/call, etc. To make it harder for opponents to figure out what you're taking each action with, you need to split your ranges so that each action is balanced. If you ALWAYS slowplay strong value and just check/call, check/call, check/shove all the time, your opponent is obviously going to know that your check/raises on the flop are weak. As such, you'll be highly exploitable.
Continuing our previous example, this is why many good heads-up hyper-turbo regs split their button ranges in half when playing other regs. They limp and min-raise polarized ranges, making it unprofitable for their opponent to 3-bet shove very light whilst still playing 85%+ of all hands from the button.
I hope I've answered your question enough to get you started with this. Balanced play and implementing principles derived from game theory optimal play so as to be less exploitable against other thinking players is quite a popular topic in poker and is actually quite complex. If you want to learn more about it, I'd suggest the following books: