Things to know: First of always make your researches, signing up is mostly for free. But before you make any investments I suggest to make a google search at first. If you find any Site I listed here as being a scam please let me know so I can adjust the information. Keep in mind what was good yesterday might be bad today!
Basics about mining Bitcoin (or any other Crypto Currency): Depending on the exchange rate of the Crypto Currency mining might not be profitable. So Some Sites can halt mining all together. (Compare it with an oil field if the Oil price is too low, it might not be profitable to get the oil out from the Oil field.). When mining the difficulty level and power consumption of the computers needed play a vital role for the profitability. You could also buy mining computers and mine from home depending on the power price you pay it might be or not be profitable.
Choosing a Mining Company/Site
Things to lookout for: Check/compare the price for the respective Crypto Currency. Check/compare the Hashrate (basicly the speed of mining). Currently check for Th/s or a very high Mh/s value when they refer to their Mining equipment. Check what Hardware they use if they still use AMD GPU’s (Grapgical processor Unit), that would be highly risky. Current machines would be called ASIC Machines they use a specially designed chip for mining Crypto Currency (and are more energy efficiant than GPU’s Look that the company uses ASIC Hardware Check what country the company is based (might be an indication for the reliability of the company) Notes: 1 Th/s = 1’000’000 Gh/s = 1’000’000’000’000 Mh/s (T = Terra / G = Giga / M = Mega) Mhash/s = millions hashes per second (double sha256 raw speed performance; may not be very energy efficient with some models) Mhash/J = millions hashes per joule (energy efficiency; 1 joule of energy is 1 watt during 1 second: 1 J = 1 W*s) W = watt (maximum power consumption, i.e. energy per unit of time: 1 W = 1 J/s)
Basics About Mining Crypto Currency
Profitability: In general when investing in mining the Return of Investment (ROI) would be around 5 to 7 month. But the Exchange rate of the respective Crypto Currency also plays a vital role. Also the Hardware the company uses (power consumption). So lets say you invest 120$ you would get per month around 20$ earnings. After aprox. 6 months you will start having a profit. Contracts: Mining companies offer different contracts for life (where you symbolicly buy the Hardware or piece/share of it). Or for a certain period like 1 year or so. This will have an effect on the price per Th/s you can buy. Check out the various contracts and make your desicion based on if you want a short term or long term investment. But keep in mind that the hardware might get obsolescent after a while due to higher dificulty level of mining the Crypto Currency.
Affiliate Program: Some companies/sites also offer affiliate programs, which can be very interesting. So always have a lookout for that and be sure to advertise it and recruit new referrals to increase your earnigs too.