If you are going make some money in Hattrick, you need good sponsors. You can get them in mood by winning matches, and they are much more steady than the supporters. However you cannot choose a sponsor as the name can suggest. Your control over this entity called Sponsor is very poor. You can enhance its value engaging some spokesman of the team.
Sponsors are one of the major sources of income for new teams as other sources of income, such as match ticket income (dependent on supporter numbers) and training regimes take time to become profitable.