35 USC 102 explained

"35 USC 102(a) THE INVENTION WAS KNOWN OR USED BY OTHERS IN THIS COUNTRY,OR PATENTED OR DESCRIBED IN A PRINTED PUBLICATION IN THIS OR A FOREIGN COUNTRY, BEFORE THE INVENTION THEREOF BY THE APPLICANT FOR PATENT"

102(a) defines that US is a first to invent country and you are not going to get a patent if your invention was known (in written form usually) or used by others (practiced) by others in USA before date of invention, and if it was patented or was described in printed publication by others in any country than also you are not going to patent.

There are some keywords like 'Others' which means other than inventor himself. If inventor himself has published or practices he might still get a patent but it was done by others than he is not going to get a patent. Keyword 'in this country' means that that if the patent was being used in any country other than USA then he might still be able to get a patent. Keyword 'printed publication in this or foreign country' means that if the invention was patented or was described in printed publication (no language bar is there so publication can be of any language) he is out of luck. The keyword 'public' means that the publication should be available to public if the publication was maintained as confidential within a company its not public but if the publication was published in a magazine in some obscure magazine in place like China in chinese language its public. Keyword "before the invention" means the date which inventor can prove he actually invented the invention and it could be before earliest filing date (if inventor can prove it with some written records).

"35 USC 102(b) THE INVENTION WAS PATENTED OR DESCRIBED IN A PRINTED PUBLICATION IN THIS OR A FOREIGN COUNTRY OR IN PUBLIC USE OR ON SALE IN THIS COUNTRY, MORE THAN ONE YEAR PRIOR TO THE DATE OF THE APPLICATION FOR PATENT IN THE UNITED STATES"

Some patent tools you must know

 Patent Library

Patent Library allows users to search by patent number and get OCR'ed PDFs of patent 

documents.

Sample Landscape reports

Patent Landscape Report on Desalination Technologies and the Use of Alternative Energies for Desalination

click here to get report 

Patent Landscape Report on Solar Cooking

click here to get report

Exceptions and Limitations of the Rights of patent - Top countries

USA

1. Solely for uses reasonably related to the development and submission of information under the Federal law which regulates the manufacture, use or sale of drugs and veterinary biological products, other than those products primarily manufactured using certain genetic manipulation techniques.
2. Certain uses concerning foreign vessels, aircraft or vehicles which temporarily or accidentally enter national territory.
3. As regards business method patents, continued use by a person who in good faith, had put the invention into practice at least one year before the filing date (priority date) and commercially used it before that date. 

Japan

1. Non-commercial use.
2. Use for experiment or research purposes.
3. Vessels and aircraft passing through Japan.
4. Products existing in Japan before the filing date (priority date).
5. Preparation of patented medicines by mixing two or more medicines in accordance with the prescription of physicians or dentists, and medicines so prepared.
6. Non-exclusive license available as of right in the case of prior use or working of the invention prior to the filing date (priority date).
7. Compulsory licenses.

India

1. The grant of a patent is subject to the following conditions:
(a) importation or manufacture of articles and uses of processes by, or on behalf of the Government for its own use;

The Scope Of Background Section

For the patent filing in US, it is good practice to minimize the amount of information provided in the Background section of a patent application.
The field of invention section is very important as if you leave this field broad , the scope can be interpreted to include more art than is actually applicable, thereby opening the patent application to obviousness rejections. an if u leave that field defined narrowly, then the associated claims may be interpreted too narrowly.
The related art in the background section is also very critical as in case of US describing any related art may get applicant into trouble. While I will sometimes list references, I recognize the risk of describing the contents of a reference in that the description may misrepresent the scope of the reference, potentially leading to accusations of intentionally misleading the examiner. Therefore, I often describe the prior art in general terms, without explicitly delineating related art references. 

It have come to know that in some countries it is necessarily to include prior art references in the Background section in response to an examiner request, and this can still be done in a revised Background section that was originally relatively short.   
I personally think that minimizing the content of the Background section in US patent applications. What are the readers’ experiences and opinions? 
Please share your views in comment section.

Searching prior art with the help of Inventor, assignee and Classification

Searching through the relevant keywords is safest approach for locating relevant prior art as there is a very high chance of finding prior art, but it is not the best approach. There are chances that some of the prior art may have been missed because of the different patent language or short description.

There are some other strategies that a good patent searcher should work out on. some of them are to use Inventors, assignees and Classifications, first of all shortlist all the closest patents you have found till date and then find their inventors, assignees and classifications (IPC, US, F terms etc). You can add some of the assignees by simply searching for the companies which are active in that field. 

Use this search engine for searching relevant US classes and use TACSY for searching relevant IPC classes. Once you have the list of Inventors, Assignees and Classifications you are ready to search.

PS: Make at-least one query which is only based on classification, and don't forget to check for the NPL that those inventors have published. You might find something interesting.

PCT VS The Paris Convention

Some advantages of the PCT are:

A single application can be filed in the applicant’s home country, in the local language.

It delays (by up to 18 months) the need to make a firm decision about the countries where patent protection is to be pursued.

The PCT International Search Report (ISR) often can help applicants determine how likely it is that the application will proceed to grant in individual countries after national phase entry.

Even accounting for the additional cost of the PCT application, slightly lower costs for national phase entry as compared with direct filings means the PCT route for more than a 

couple of countries can actually be cheaper overall.

Typical PCT Procedure: