Wee dictionaries are a good way to build your basic vocabulary.
The next step is the Essential Scots Dictionary, designed for learners.
There is a free app version of this dictionary, too.
From the same stable, but a little more comprehensive and useful for writing is the Concise English-Scots Dictionary.
Once you are about this level, the Online Scots Dictionary is very useful and popular with writers, from Scots to English or English to Scots. An Android Scots Dictionary App is also available via Google Play.
For more advanced scholars the Scots to English Concise Scots Dictionary (now in its Second edition) is a treasure trove.
The Scots Thesaurus should also be on any writer’s shelf.
Finally the DSL Online contains the motherload of ancient and modern Scots vocabulary, but if you are a new writer needs to be treated with some caution!