It would be advisable to use some kind of mixing service (bitcoin fog - only accessible via tor, or bitmixer.io - accessible via the clearnet) after you purchase your coins on an exchange.
When you go go spend your coins you should use a VPN or TOR to mask your IP address as the person who sent the TX.
Can you guys please explain how this works ? Would like to use either one of the methods suggested but i don't have a clue. I'm new to using btc
If you go to bitmixer.io (search these forums and google to make sure you can trust them) you simply click on, add foreward address and past in a BTC address that you control but have not yet used. I would recommond clicking on "add one more foreward address" for added anominoty at least once to add an additional foreward address. You select the time delay that you want the coins to have before they send it to you.
You will then click on mix my coins and there will be an address to send the coins that you want mixed to. At the bottom there is a letter of guarantee that you will need to open and save in case there is a problem. You then send the coins that you want mixed to the address provided and bitmixer will give you new coins that are not associated with your previous coins at the addresses that you provided them.