As the property market is widely considered to be one of the best places for long-term investments, not to mention the fact it offers attractive returns thanks to low-interest rates at present, building a commercial real estate portfolio is often an ambition for many private investors.A common-sense approach, thorough research and investing in properties and locations with good market demand and long-term appeal can help you drum up significant profits.But where do you start and how do you make sure you're making all the right decisions when it comes to your commercial properties:Important considerationsEven though the commercial property market does come with a more favourable tax regime, there are still some pitfalls you'll want to watch out for. For example, you'll need to pay attention to lettability and location as there's often more buildings looking for fewer prospective tenants.Obsolescence is also something that'll need addressing. EPCs need examining closely because if a building doesn't meet up to the necessary standards you might not be able to sell it or let it out, while works to get it to the right standard may be costly.You should also think about whether you want properties in industrial, retail or office sectors.Invest in what you're familiar with If you live in a city, the chances are you've got a good all-round knowledge of the local property market and what areas are bad, good or up-and-coming - so use this knowledge to your advantage instead of looking in areas you aren't familiar with at all.Consider the micro and the macroThink about whether the economy's generally improving, what effects things like Brexit could have on the market and whether the demand for your property could be affected by wider market forces. Your finances may also be impacted by inflation and interest rates, and this may affect your tenants, too.Look to the futureIf the market takes a turn, do you have a backup plan? If your tenant vacates the property, is it going to be easy enough to find someone to replace them? If not, could you potentially change the building's use to meet another more demanding niche? When it comes to selling the property, who's your potential purchaser going to be?Research, research, researchFinally - do your homework. Research the market in depth, speak to local agents, look at recent rents, deals and stats for similar properties, investigate local developments and how they could affect your asset(s) and carefully calculate expected returns and costs to make sure all of the figures add up before you sign on the dotted line.