Here are some tips:
1) Do not invest only in Bitcoins, diversify in alt coins as well.
2) Do not panic when prices fall by 30% or so in a day.

January 2018 had been unfortunate for Bitcoins but there is lot of time left. I think we will see prices recover soon.

Wait for a few months, I think it will reach to the level of $5000 or so. Then it will be the right time to invest in my opinion.