how to solve AJAX HTTP error 200, when try to manage field display & Views?

This problem usually we face in 3 scenarios for drupal
1. when we update Jquery Update to new version. This scenario we can easily solve it by reverting back to old version.And be cautious, while doing any updates in drupal, try to do it in test environment later try in rela time.
2. When we try to fulfill our requirement by hard coding like adding .js files manually instead of using modules. To solve this, our first step is we need to find by which file adding we are getting this error.So try to remove each js file which you added manually and test at admin side still problem persists or not?(Don't forget to remove cache for each trial). Continue this until problem  solved.
3. Sometimes when we install some new modules also we face this problem, because sometimes the js files which are used in new module may be not adjusted to old module js files. So uninstall newly added module and check again.

how to solve blank pages or "white screen of death" (WSOD) in drupal?

This issue will come generally because of allocation of memory in mysql, to over come this just run the below query in mysql server.

mysql> SET max_allowed_packet = 1024 * 1024 * 512;

or

mysql> SET global max_allowed_packet=1024 * 1024 * 512;

How to solve Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone in Drupal 7?

This issue will come generally because of allocation of memory in mysql, to over come this just run the below query in mysql server.

mysql> SET max_allowed_packet = 1024 * 1024 * 512;

 or  

mysql> SET global max_allowed_packet=1024 * 1024 * 512; 

How to Solve Notice: Undefined index: highlighted in include() in drupal 7?

To solve this error/notice need to follow below steps.

1. If you have created any block or region need to check the block/region name in .info file of the theme. For example i have created on block/region like..

how to add/create a new block in drupal?

To create a new block region just need to following things..
1. In .info file we need to add block name like..
     regions[sidebar_second] = Sidebar Second
2. Then goto template page and add the below code wherever you want add the block of region.
    <div id="right1" class="clearfix">
            <?php print render($page['sidebar_second']); ?>
     </div>
Note: need to give div id unique

How to Add CKEditor in Drupal

Following Steps need to follow.

First Download 3 file.

1. Download CKEditor module(ex.ckeditor 7.x-1.2). To download click here.
2. Download CKEditor Software(ex.CKEditor 3.6.6) .To download click here.
3.  Download imce Software(ex.imce-7.x-1.4.tar.gz) .To download click here 
4. Unzip all the zip files which are downloaded. After that copy the CKEditor software folder. 
5. Inside the CKEDitor module folder there is folder name CKEditor, paste the software folder in that folder.
6. Now copy the CKEditor module folder and IMCE folder into the drupal project folder in sites/all/module.

How to remove Read more and display Content on front page

Just goto Configuration -> Site Information there we will find an option like "Default front page". There you can give your node id of the page what you are created.


For Ex.


I have created page which i want to make as front page like "Wel Come". When we are created the page it will take a node id a default value like "5".


So we need to add this value in Default Front Page as "node/5"