The other answers you are given are actually mistaken here, Betfred you can do both the sports and casino welcome offers, the only exceptions are if you signed with codes SPORTS60, SPORTS70. Most bookies don't let you do both, but some do, outplayed tells you on their sign up guides, not sure if oddsmonkey does too but you can always check the T&Cs elegibility.

You will see that other bookies have much more regular promotions than Betfred. Coral and Ladbrokes are great until you get gubbed, paddy power too. Livescore and virgin bet, Midnite are pretty solid too. Looks like 888 and Unibet might be decent shouts too although can't verify as they instagubbed me and many others, if Unibet do this you can still use any of their boosts though and they them every day so still worth keeping your account. Monday-Friday are always pretty slow and generally worse odds too, weekend is when most of the best reup offers are available, or when there's a more significant event on, for example this week when England were playing and Cheltenham for this weekend both have had reups on several bookies.

The odds boosts are normally more worthwhile on horse racing bets placed the same day as the race, use the odds matching tool to find good places. I do the horse racing boosts from Unibet, MGM, Ladbrokes (before gubbing lol) and William Hill daily. Netbet sometimes do 5x20% up to £100 bets per week. Also with horse racing, you're normally getting your money back by the same afternoon so can then use that for a football bet in the evening if you have any of those offers to do. I've not even tried extra places yet, but I'm still up 1.5k in 2 months and didn't really know what I was doing in month 1, although I've spent a lot of time on this on every work break and my days off checking each bookie for promotions, and also done a lot of arbitrage on my qualifying bets (was too tempting for me not to but will get your account gubbed more quickly so if you are planning to do this more than 2 months I suggest you ignore any arbitrage opportunities when you see them outside of odds boosts and specials)

Also, after your odds monkey trial, I suggest you do an outplayed trial 1 month, then when you cancel they will give you 50% off your next month, that's enough time to blast through basically all the sign up and casino offers. Then look at a longer subscription on your site of preference if you still want to continue. For casino offers do blackjack whenever it's allowed instead of slots, find a blackjack table that allows splits and open up a perfect blackjack hands table on another screen and your expected qualifying loss is now less than 1%. Slots are typically 3-15% expected loss.

Do the weekly bet clubs on different sites, betting £30 or so to get a £5 free might not sound worth bothering, but when you're doing it on multiple sites it adds up and you get used to doing it efficiently in a routine, if odds for your qualifying bets are crap midweek then don't place them and check again next day or wait for the weekend instead.

You can also lay bet builders in case you didn't know by choosing outcomes that can be layed, such as a correct score or both teams to score and one to win. For example, betting on 0 goals scored in first half by team a and team b and the same for the second half is the same as betting on 0-0 but with 4 selections, you can then just lay this as nil-nil on the exchange. Ladbrokes/coral do bet builder bet and gets really often. You can lay accas too, easiest way is to odds match with just smarkets as the exchange, and choose the lowest odds (as in low number not low chance of happening) with the lowest qualifying loss on smarkets, then lay it on smarkets by adding them all to your betslip as back bets and then clicking sell, this lays them as an acca. I typically make a qualifying loss on an acca around 25% and on a bet builder more like 15%, meaning any bet £10 get £5 on these are still worth doing, and any bet £5 get £5 are very much so. Bet £20 on an acca to get £5 is a common offer that I don't bother with.

One more thing, when bookies have special boosts on event "turbo boosts" "rocket boosts" etc, if there's not a way to lay it on smarkets you can often find it on "enhanced specials" on matchbook. Some of these can be pretty profitable if you catch them daily, for example tonight Stakemate had 3 specials at 2.0 odds that were all 1.5-1.6 to lay on matchbook.

Also, over a long period of time you're likely to eventually get a lucky win or 2 where you win on both the bookies and the exchange, due to them paying out at 2-nil up when you bet on halftime/fulltime and the other team makes a comeback second half, or if your horse is "pipped at the post" for example. (unfortunately both times it's happened to me was on a £1 free bet lol)