Keep your luggage closed at hand at all times and in sight if possible. Do not have your name or address visible on any tags and never leave your luggage unattended.
Find out about the different cultures and laws where you plan, English speaking countries may have the same language but have very different laws and customs to the UK.
If travelling in a big city, study the public transport system, its the quickest way to get around but can be confusing.
To avoid unwanted attention, try to blend in be polite and respect the local laws and customs. Dress more conservatively than you maybe would at home, this could ward off opportunists.
Take out only what money you think you will need for the day, having a wallet full of cash can attract unwanted attention. Its an idea to keep an extra note in a small pocket just in case anything happens and your wallet is lost or you see something you want to buy.