The answer to all these questions can be given very simple; you don’t just need lots of them, the best, the most expensive. You need all of them!
Here is what you should NOT do while going out to get those links:

• Do not forget to check your internal links. All webmasters know that links are important. Some work hard to get those links, some focus on quantity, some on quality, but many fail to check their internal links. Internal links are the most important links on a site and what is more? You have them in control! Check if you used relevant anchor texts and positioning of those links.
• Do not forget to get some low PR links. Because everyone is looking for the quick fix and tries to get links from high PR sites, many webmasters forget to look on a long term basis. Those PR0 sites are very easy to give a link to you, and some of them will the PR4 and PR5 sites in the future. Besides that there are two more reasons to get the low PR links as well: PR0 is not nothing, it all counts. And it is more natural to have incoming links from all kind of PR sites.
• Do not forget your outgoing links. Don’t worry about PR juice leaking away. You can see it in two ways: each good article or statement shows the source of the information. And if you want to get something, you need to give something.
• Do not forget to monitor your inbound links. If you have done a links exchange, content exchange or bought a link or won a link, check regularly if it is still in place and if it is a real do follow link. When you have done a trade, don’t forget about it as soon as it is put up. Monitor your link partners.
• Do not use useless anchor texts. If you have the opportunity to choose an anchor text, use a relevant keyword for it. It is a big failure to just choose your URL or company name as anchor text. It is very likely that nobody is searching for that. Find out your keywords under which you want to rank and choose that as an anchor text where possible.
• Do not leave paid linking marks. Even though paid linking is not recommended, it still works in many cases and the temptation will always be there. Just make sure that you do not leave big marks behind that are easy to track. Do not make it too obvious that you are paying for links.
• Do not forget to check the relevance of a link. There is not much point in receiving links from totally unrelated websites. Try to focus on sites with a related or similar topic to get your links from. And get some real links from that site, not somewhere from the 20th page of their link exchange program. PR isn’t everything, relevance and positioning are.
• Do not add ‘no follow’ to your outgoing links. Just as you expect a genuine link to your site, you should give genuine links as well. PR juice is really not leaking to anywhere if your links are genuine. Only pages that consist of links only and are irrelevant to other pages will lose their PR very quickly, but this has nothing to do with a leak.

Link building is a very time consuming and frustrating job. Remember: nobody really likes it. You send out 100 emails, fill in tons of forms and receive only a handful of links back. That is the way it is, but if done right, it is totally worth it. Good links will last a long time.

• An SEO expert analyses your website. In order to do an effective job, he needs to really understand your website, know how it is structured and what the important webpages are. The expert needs to get a clear picture of the site as a whole.
• A good SEO company will conduct a keyword analysis to find the most relevant keywords for the website, to see which keywords are searched for and could drive targeted traffic. Also competitiveness should be analyzed. There are some less competitive keywords that still drive a lot of traffic, but could be easier to optimize for.
• Then the SEO expert will check the rankings of the website under the targeted keywords found in the previous analysis. This is to see where the site is ranking well and where not, so that the expert can see which areas need more attention then others.
• The websites that are currently in the top positions of the targeted keyword searches should then be checked out; what is their structure, title, number and quality of backlinks, etc. In other words, finding out how they got to that top ranking.
• The expert will have a look at the most important landing pages of your site and evaluate the content of it. Factors as keyword density and keyword prominence are included in the evaluation. Pages might have to be re-written.
• An SEO company also looks at the coding of the site. Search Engines see the website from a totally different point of view than the visitors, but this should be synchronized as much as possible.
• Before barging on a course of changes, the SEO expert will have to give an overview of his findings and make recommendations to optimize page elements, coding, meta tags, etc. This way it can be established that the SEO is working in the right direction and following the objectives of the client.
• Internal and External link structure are a major factor in the search engine’s algorithms. The SEO expert will examine your internal linking and start an external link building campaign with creative ways to build highly relevant incoming links.

An SEO expert will regularly track results of the implemented strategies, update the ranking reports, reflect on them and if necessary make new recommendations. It is also the task of an SEO expert to keep up to date on search engine rule changes and competitive site rank changes and respond to that.
SEO is an ongoing process and has most benefits if handled as a whole. Your SEO expert should have a good insight in all the factors and changes involved and implement strategies accordingly.