There is a “hobby loss” rule that limits deductions attributable to an activity not engaged in for profit. If the activity is not engaged in for profit, the taxpayer may deduct, in the following order (Sec. 183)

Those items whose deductibility does not depend on a profit motive, such as interest, property taxes, and casualty losses
Items deductible only if the activity is engaged in for profit (other than depreciation), but only to the extent that the gross income from the activity exceeds the deductions allowed
Depreciation

In other words, if the activity is …

A deduction for the business use of a personal residence is allowed only if the space is used exclusively and on a regular basis as any of the following:

The principal place of any business in which the taxpayer engages. A home is treated as a principal place of business if it is used for substantial administrative or managerial activities and there is no other fixed location for the performance of these activities.
A place of business used for meeting clients, customers, or patients.
In connection with the taxpayer’s trade or business if …

Unreimbursed employees’ business expenses are miscellaneous itemized deductions and are deductible from adjusted gross income, together with other itemized deductions. Again, the expenses must be “ordinary and necessary” and “reasonable” in amount and exceed 2% of adjusted gross income. Such expenses include the following

Union and trade-organization dues and convention expenses
Work clothes, including cleaning and laundry
Small tools (if useful life is less than one year; otherwise, a depreciation deduction is available)
Subscription to trade and technical journals and newspapers
Hiring of assistants and substitutes (if not paid for by employer)

The cost of work …

* If you have 1 job, you cannot deduct commuting costs because it is considered a personal expense, not a business expense.
* If you have 2 jobs or 2 places of business, you can deduct the cost of traveling from the frist one to the second one. 
* If you claim home office deductions for a home-based business, you can deduct the cost of going to and from home to another business location or a job since the home is also a business location. Hint: keep excellent mileage records.
*  The mileage …

* If you’re on the road for just a day (no overnight), the cost of your meals is not deductible. So, if you travel on businesss to a nearby city, you can only deduct the cost of transportation not the cost of meals or other traveling expenses. Hint: if you meet someone for a meal, the cost may be deductible at 50%.
* You can deduct the cost of travel only if it is an “ordinary and necessary” business expense. You can deduct travel expenses incurred in attending a trade, business, …