The actual steps that you need to take as you plan and research will vary considerably according to your own position are you importing or exporting?  Raw materials or finished goods?  Permanent supplier/market, or seasonal one?  I would suggest, however, that the following should appear in most, if not every plan.

1. A short summary rationale as to why you are looking to trade overseas e.g. source cheaper goods, find new markets.
2. Is this on-going or seasonal?
3. If known at this stage, the Country/Countries that you want to trade with, again, with a rationale as to why these Countries and not others.
4. Again, if known at this stage, how you intend to control the overseas part local representation, agents, joint venture?
5. How do you intend to research the chosen Country/Area?  Fact finding missions and trade fairs are but 2 possibilities.  Can any other businesses who have been down this road before assist you?
6. The legal status of any agreements to your new suppliers/buyers.  Formal contracts?  UK or local [foreign] law?  Obtain suitable legal advice preferably before you commit to anything.
7. Trade terms.  You may not know at this stage, but part of any agreement/contract that involves the shipment of physical goods will include what are known as INCOTERMS.  These define which party is responsible for the goods at each stage of their movement from supplier to buyer.  If you are involved in a service related trade, you need to consider at what point the service has been delivered and, therefore, payment is due.
8. Consider whether there are any import/export restrictions and/or tariffs/quotas on your goods/services both from the perspective of the UK and the foreign Country.  The UKTI website is a good source of information here.
9. For physical shipments, do you need to consider how they will get from A to B?  Do you currently have a Freight Forwarder?
10. An acknowledgement of the fact that local business protocol may be very different from that seen in the UK.  You need to understand this before you embark on any visits/negotiations, even those at a distance, e.g. telephone/internet.
11. Is there a language issue to consider?  English may be the language of business, but its not universal! 
12. Impact on cashflow.  DO NOT OVERLOOK!!  This is a complex and critical area, covering many aspects and much thought [and, usually, help] is needed here again, preferably before you commit yourself to anything.  Doing business overseas can make the usual payment cycle longer if youre selling, or shorter if youre buying.  Either way, these can have an unexpected and unwelcome effect on your cashflow.  Areas to consider include:
1. Item price.  It needs to be fixed based on the local going price, not the UK one.
2. Currency.  It may be more convenient for you to price in Sterling, but often the local currency is better and will give better results.  For some countries, e.g. China, Africa and much of S America, a 3rd currency [typically US Dollars] may be appropriate.
3. Foreign Exchange Risk.  If trading in a foreign currency, you need to consider what approach you are considering re exchange rate movements.
4. Terms of Payment.  Not just what credit [if any] are you giving/being given, but how are contracts to be settled.  Putting a cheque in the post is not recommended, not least as its very insecure.
13. [If youre importing], quality control of the goods.  How is this to be managed?  A similar issue may arise for exports, but your usual concern here is getting paid!
14. Consider the need for any specialised legal assistance e.g. around Intellectual Property Rights.

Good Luck!

Ray Stannard, International Trade Financial Solutions.  Tel/Fax 01708 370838, Mobile 07768 903258, e-mail ray@inttradefinsolns.co.uk   www.inttradefinsolns.co.uk.

Minimising Commercial Risks When Trading Abroad.