Hi, I am very new to this field. I can do off pageSEOactivities with good practice but now I want to learn all on page tactics for*SEO. Please help me from where I should start and which steps I should follow?
Check out this FAQ:
It will get you started nicely. 
Try the book “SEO for dummies”. I read the book and implement the tactics in my website, and my traffic almost triple in 3 weeks.
Off Page Optimization is all about things you could do to get better ranking of your keyword and to increase PR. If you have complete keyword research and are clear what keywords you want to optimize, you need to develop strategies that help in improving ranking of these keywords. Off page include steps which you actually execute outside the pages of your website. Now what are these steps? All these steps concerned with link building strategies.
Link building has become so important to improve search engine positioning. There are many different ways of getting back linking.
- Article Submission
- Forum Posting
- Directory Submission
- Blog Commenting
- Press Releases
- Social bookmarking
you didn’t read his original question, did you 
You are right i miss that but how here is one good tip for keyword selection…
Selection of right keyword is first step in On page optimization, there are many tools which helps in getting right keywords like Google adword tool, Google keyword suggestion tool, select right keyword that is relevant to content and use it in content.
Important thing
• Research: Do a proper research before you decide on your keywords.
• Keyword Density: Try to have a moderate keyword density so that it can help the search engine to determine that your page is indeed related & relevant to the keyword that you are targeting.
• Long Tail Keywords: It’s often good to target some long tail keywords as they are comparatively easier to rank for.
• But you can also come up with your own long tail keywords; for example try adding some common words like ‘best’, ‘free’, ‘cheap’, ‘top’ etc. along with your actual keyword and you might eventually get some good long tail keywords.
Put the keyword phrase into the title tag of the HTML document.
Also, put it into the following:
<h1> tag
meta description
meta keywords
and a few times in the content