When using early printed material and archives, always be aware of thier source and the reasons that they were created. By doing this, you will soon become aware of the potential and limitations of different records.
Another golden rule when planning your research is to always start with recent records and work backwards, methodically, towards earlier ones. This will allow you to establish a clear chronological sequence to your research and lets you become familiar with simpler records and handwriting styles before tackling earlier material, which tends to be more challenging.
Reading old documents can be difficult because of their language and handwriting. For instance, early Scottish documents may be written in Scots or Latin. They are often heavily abbreviated and use letter forms that we are no longer familiar with. The practice of reading old handwriting is called palaeography - useful aids include:
An online tutorial focusing on Scottish handwriting in the period 1500-1750 - still useful, even if your research is based on later documents, as it provides useful context and background.
The Scottish Record Association Scottish Handwriting 1500-1700, A Self Help Pack (Edinburgh, 1994). This pack contains examples of common types of document found in Scottish archives with transcripts and notes.
Alf Ison, A Secretary Hand ABC (Berkshire Family History Society: 3rd ed 2000). An excellent introduction and guide to reading documents written in Secretary Hand, the style most commonly found in documents up until the early 19th century.
Grant G. Simpson's Scottish Handwriting 1150-1650 (Edinburgh, 1973). A guide to early Scottish handwriting. Best not to attempt this one until you have mastered the later hands.
A useful source for trouble-shooting difficult, obscure or archaic Scots words is the Dictionary of the Scots Language (DSL) This very useful website incorporates the twelve-volume Dictionary of the Older Scottish Tongue (DOST) and ten-volume Scottish National Dictionary (SND)
The Oxford English Dictionary is also a valuable tool - particularly the multi-volume sets that you should find in good reference libraries and archives.
Finally, remember that old records and early printed books are fragile and must be handled with great care at all times. For this reason, most archives ask their researchers to comply with a short series of rules which reflect good handling practice. These normally include using pencils rather than pens, not leaning on, folding, or marking items, and not eating or drinking in research areas. Sometimes items may be too fragile to use and you may be refused access to them for this reason.