Have an up to date Writers and Artists Yearbook to hand.
For the listings, for the fact they don’t include those that might charge for publishing (no mention of Pegasus Elliott Mackenzie!) and for addresses, editor names etc.
Have subscription to Writers’ News/Writing Magazine.
For good advice on all writing issues, for competitions and news of markets, especially short story ones. To learn something of what is going on in the industry (though for more details it would pay to subscribe to The Bookseller or as I do visit their website often). There are other writing magazines out there but this is the one I read most often. Mslexia is useful for their wonderful diary, short story comp and writing from a women’s perspective but Writers’ News gives a wider range of markets.
Don’t expect to get your work right first go.
Nobody does. Practically everything writing wise is improved by a darned good edit!
Have reference books to hand
By which I mean a diictionary, thesaurus, Brewer’s Phrase and Fable, Chambers Book of Facts, a history, book of proverbs, Bible and so on. Obviously for checking facts but also for direct inspiration. Many a short story has come out of an old proverb! Bible stories like Samson and Delilah can inspire a modern take on that – the themes of love, jealousy and betrayal are universal. Brewers makes for a wonderful read given it gives the source of phrases and fables.