e.g : Transient Integer tempVar ;
Some apex objects are automatically considered transient, i.e thier value does not get saved as part of page’s view state. These objects are SavePoints , PageReference, XMLStream Classes etc. Static variables also don’t get transmitted thorugh the view state.

Third: 

//Fetching account records
List accLst = [Select Id, Name From Account Limit 10000] ;
//Creating new map to hold id as key and Account name as value
Map accountMap = new Map() ;
//Putting Id as key and account name as value in map
for(Account tempAcc : accLst) {
     accountMap.put(tempAcc.Id , tempAcc.Name) ;
}

Best way to write query in for loop to avoid filling space of heap by creating a list like :

for(Account tempAcc : [Select Id, Name From Account Limit 10000]) {
    accountMap.put(tempAcc.Id , tempAcc.Name) ;
}

or if we are creating a list to hold account records then we can nullify the list after using it in for loop like :

for(Account tempAcc : accLst) {
   accountMap.put(tempAcc.Id , tempAcc.Name) ;
}

//To reduce heap size
accLst = null ;

Misc steps :
1) Exception handling
2) Commenting
3) Change history tracking (keep history of the changes in class)
4) Query should always contain LIMIT