First of all any new trader to the Nasdaq is ill advised to trade pre and post market on an ECN becuase the liquidity isnt there and its not as easy to manage your trade.The most liquid ECN is probably Island and i would suggest its worth getting used to using it during market hours first.
If you want to trade the island book pre or post market i suggest that first you work out your stratergy and then see if your stop is attainable should things go wrong.
Next i suggest that you become an expert at reading the island book and become like a panther in watching,waiting and hiding in order to get your fills.
I said hiding becuase island offer hidden island orders,is your software offering them?because the majority dont and it can be another little edge in your armoury.
Next you need to decide on which side of the book you wish to deal, the bid or ask.If you wish to take your trade on the ask,set your trade up and sweep the book as some one comes in and closes the spread,keep looking and watching getting into sync with the flow.
So maybe you want to save the spread (which can be worth doing in after hours trading) and want to buy on the bid.Now it all depends on the liquidity as to what your plans are.But if its slow check out what the moves are first and then hide your order $.004 above the price you want to get filled at.Why, because otherwise you will be in a queue at that price and everyone else will get filled before you.Doing this puts you at the front of the queue and its hidden so no one can see you. If you showed your order then players might jump infront of you giving you less time to fill your order.Why .004 because there might be another hidden order there and you've just jumped infront of him.
So now someone out there wants to sell some stock and the order routes to you first.If you want to buy a 1000 shares this way, on the bid, then you will only get filled for the amount that player wishes to sell. If its 1000 great, if its 23 then so be it.All the time you're best bid, orders are routed to you and your 1000 share order will get filled.At any time you can hit your hot key and cancel whats left of your order and work with what you've got.Check with your broker on fees for fills and the timing limits for partial fills.
Remember anyone astute enough in that queue can look at the time and sales and realise after the event that someone was hiding and got a fill.Will he then increase his bid and move above you.If he or anyone else does, orders will route to them first and your order flow will dry up.What is your plan then? If you are partialy filled for 23 shares whats your plan for that?
Remember that this is direct access,you can now operate like a market maker and cut down on your costs with better fills.But you have to think slightly differently. I would suggest that working the island book with a SMALL number of shares in the first instance in a liquid environment and getting proficient with it, making quick decisions and reading the screen would help in the initial stages.I also advise sitting with some one who trades level 2 Nasdaq in the first instance to learn how to work your order for better fills and to also save making those first costly mistakes through lack of knowledge.