What is the proper explanation about website or project performance?

While Implement any application we need to concentrate performance also. To improve performance we need to concentrate on several factors. I will share you few of those.

DataBase Wise:

1) Proper indexes in a table
2) Use Proper relationships between tables.
3) while querying try to avoid unnecessary fields, instead of * use respective fields (columns).
4) Try to avoid aggregate functions and Grouping clauses.
5) Instead of temporary tables use CTE.
6) Use proper joins, and try to avoid nested queries
7) While joining first call master table then child table, because master table contains limited records while searching its look at limited records.

Application Wise:

1) try to avoid unnecessary code blocks
2) Avoid to load all the records while loading time, instead of that load based on filter.
3) Unnecessary don't use nested looping and looping, if it's required then only use.
4) Always use light weight controls.
5) Try to reuse code blocks, instead of create new.

Apart from the above you need to look at Server, RAM, Hard disk etc...