The first problem is to determine if there are any notarial records that might help your research. Since there seems to be no general index, and since notaries could in principle record documents anywhere within the territory of Vaud, some guesswork is involved. The approach that has worked best for me is the following:
Short answer: a little at a time!
Longer answer: There are several problems to be overcome. First, the state of preservation of the documents may make sections completely illegible, for example from bleed-through, so that the writing on the back of the page has obscured the writing on the front. In such a case, I would not recommend spending a lot of time with the document, because any information you glean from it may be the result of misreading. Second, the handwriting and personality of the notary (or of his clerks, it is common to encounter several different hands in a volume of notarial records) are unique. Each notary has his own style, including handwriting and abbreviations. Third, even when you can make out most of the words, the legal jargon of earlier centuries can be extremely difficult to penetrate. The problem of comprehending some of the documents found in these records far exceeds the difficulty of understanding the typical American mortgage!
In spite of these problems, the records of most notaries can be useful for genealogical research. Each notary may be different, but you will benefit from having studied the church records first to get used to the handwriting of the period and also the surnames and place names of the area. The names you recognize are the Rosetta Stone for decoding the words that are harder to decipher. Sometimes it pays to look over the whole volume first for clues about how the material is organized. You may be able to find documents scattered through a volume that evidently pertain to the same legal issue (for example, a particular inheritance), and comparison of these documents may eventually turn up a clearer reading of a doubtful phrase.
Abbreviations and shorthand may be hard to penetrate. There are special forms for certain syllables: a large "p" representing "pro", "pre", or "per"; a large "q" representing "con" or "com"; a "d" with a descending stroke below the line at the end, representing "dit", "dits", "ditte", or "dittes" in compound words such as "prédit" ("aforesaid"); various hooks, loops, or strokes at the end of a word representing any number of omitted syllables. Click here to see some typical short forms.
In the registers containing "actes de notaire" (as opposed to the "minutaires" or minute books), there is frequently a summary title for each document. When in doubt, copy the title, which should at least name the buyer. When the title lists both parties, it is normally the buyer who is listed first, then the name of the seller, separated by the word "Contre". There is, however, no requirement that the title include all of the parties!
In the body of a document concerning the sale or donation of property, the seller or grantor is normally listed first. In fact, such documents are very similar to modern deeds (and just as dull), having the form, "Jean Favre, knowing what he is doing and informed of his rights, sells, cedes, quits, and transfers to Joseph Favre the following property, towit...", followed by a lengthy description of the property, the price, and a series of clauses that make the transaction binding. The document usually closes with the DATE and the names of two or more witnesses. What makes these documents more interesting is when there are notations about the relationships or circumstances of either the buyer or the seller. The seller may be acting in the name of his wife or of some other person (relationship frequently noted), and may have some relationship to the buyer. The transaction may relate to a dowry, a debt, an inheritance, or a judgement of some kind. The genealogical meat of the document is apt to reside in these details.
Watch out for a series of documents where the buyer or seller is listed only in the first one of the series, the other documents referring back to the first one by a phrase such as "Le vendeur comme dessus" (the seller as listed above) or "Le prédit" (the aforesaid). It is also common for dates and witnesses to be carried forward to multiple documents by similar phrases indicating "the same date as above" or "the witnesses as above".
Always note how each party is identified. Is he a "bourgeois" of a particular town, or is he simply living there? Is his occupation listed? Is he listed as the son of someone, if so, is that person noted as deceased?
Notaries recorded all sorts of contracts, transactions, and debts, ranging from payment for a wheel of cheese to the transfer of feudal rights. (Link: The Duties of a Notary.) Here are some of the types that I have encountered:
A complete understanding of a complicated legal document from the 16th Century may be no more helpful than a detailed understanding of a 20th Century American mortgage document! For genealogical research, the details of a document about property transferred between individuals may be unimportant; the significance of the document may simply be that it proves your ancestor was alive and in a particular place on a given date.
However, in documents relating to marriage or inheritance, the details may contain information about previous generations. It is helpful to develop at least a little understanding of the legal terminology of the period. Particularly under the feudal regime, the legal vocabulary does not seem to translate well. Some of it can be worked out from contemporary dictionaries. There are a few scholarly accounts of the documents relating to marriage and property, but they are almost as obscure as the documents themselves. When a document seems important, and you can transcribe most of it, but still fail to grasp the nature of the transaction, it may be helpful to post the details on the Vaud query page in hopes that someone with more experience can help you interpret it. Also, since many old legal terms in the French language are derived directly from Latin legal terms, you can sometimes find enlightenment in a good legal dictionary.