If you have a large Gmail box you will indefinitely need to do some search function to find an particular email.
The first thing you should do to categorise and store important emails are to create Labels and assign the emails to these labels. But time to time you may want to search the mail box to find emails so below are some tip in your searches to narrow down what you are looking for.
To search within email in a label use... label: {Label1 Label2} for single word labels
... label:Label-Three label:Label-Four for mutiword labels
To find exclude messages from the labels... -label:Label1
To search for every message that has a label... has:userlabel
To search for every message that has no label... has:nouserlabels
To search emails with attachment.. has:attachement
To search in combination... email: This email address is being protected from spambots. You need JavaScript enabled to view it. has:attachment
To search with filename... email: This email address is being protected from spambots. You need JavaScript enabled to view it. filename:jpg
For more info on general Gmail search tips click here. For tips on specific search tips click here.