A few ongoing offers that i can think of are:-

Free Scratchcards - Daily
B365 4/1 Offer - Daily
SJ Chips - Weekly
Beat Vic - Weekly (usually)
Blue Square Predictions - Weekly
Jaxx Points - Monthly
Coral Cashback - Monthly
Blue Square Fair & Square - Occasionally
IW Arbs - Whenever there's lots of footie on!

So obviously it's worth getting accounts with all the above asap. Other accounts worth getting asap:-

Hills - Regular Bogofs
Bet24 - Plenty of offers/reloads
Betclic - Plenty of offers/reloads
Eurosportbet - Plenty of offers

Learn spread betting (make sure you really know what you are doing) - the offers are very lucrative, plus Sporting Index have regularish offers for existing customers.

I only matched bet part time, as i have a 9-5 day job at present, so frequently find i don't have enough spare time to do every offer. What i try and do, is prioritise based on which offer is likely to be most lucrative/easiest.

I tend to write a list each week of all the offers i am or might be interested in. I then put a star next to any really good ones, and a question mark next to any that might not be worth doing. I then cross them off the list as i do them.

As well as organise offers, i also TRY to organise my time. For example the competitions can be entered at any time, whereas best time to look for arbs is in the 3-4 hours before games kick off. Also consider how much time it is really worth spending to find a a match - If it's only a small bet, then the difference between a narb and an arb might only be a few pence, but if you're placing a large bet for say the Coral 10% then spending more time finding a better bet will be worth it.

Final point, is echoing what Super_Dash said - make sure you understand what you are doing and why/how it works. I still usually write down my 3 way grumbler dutches, and work through each outcome using a calculator, to make sure that it works (i'm always amazed it does)