Within your Invest Direct account, you can see live market data. You can see this by typing the stock name/ticker into the search box up the top. This will assist you with choosing your limit price and viewing the orders placed in the market.
Looking at this example screen can help you decide what price level to place your order at. You will see 'the spread' at the top of the depth, which is the difference between the highest bid (buy order) and the lowest offer (sell order).
If you want to get your order filled immediately (if you're buying, you could place it at or above the lowest ask)
This means that as a buyer, you could place an order at $8.70 and your order would be filled immediately, provided that you're buying less than the amount shares available in the market at that price. Alternatively, because the top buyer in the market is at $8.50, you could put a price of $8.60 and become the highest bidder in the market. From there, you can hope one of the offers amends their price down to you or another seller comes into the market and is happy to offer your bid price.